HS7.9

The atmospheric water cycle under change: feedbacks, land use, hydrological changes and implications

Traditionally, hydrologists focus on the partitioning of precipitation water on the surface, into evaporation and runoff, with these fluxes being the input to their hydrologic models. However, more than half of the evaporation globally comes back as precipitation on land, ignoring an important feedback of the water cycle if the previous focus applied. Land-use and water-use changes, as well as climate variability and change alter, not only, the partitioning of water but also the atmospheric input of water as precipitation, related with this feedback, at both remote and local scales.

This session aims to:
i. investigate the remote and local atmospheric feedbacks from human interventions such as greenhouse gasses, irrigation, deforestation, and reservoirs on the water cycle, precipitation and climate, based on observations and coupled modelling approaches,
ii. investigate the use of hydroclimatic frameworks such as the Budyko framework to understand the human and climate effects on both atmospheric water input and partitioning,
iii. explore the implications of atmospheric feedbacks on the hydrologic cycle for land and water management.

Typically, studies in this session are applied studies using fundamental characteristics of the atmospheric branch of the hydrologic cycle on different scales. These fundamentals include, but are not limited to, atmospheric circulation, humidity, hydroclimate frameworks, residence times, recycling ratios, sources and sinks of atmospheric moisture, energy balance and climatic extremes. Studies may also evaluate different sources of data for atmospheric hydrology and implications for inter-comparison and meta-analysis. For example, observations networks, isotopic studies, conceptual models, Budyko-based hydro climatological assessments, back-trajectories, reanalysis and fully coupled earth system model simulations.

Co-organized by AS1
Convener: Ruud van der Ent | Co-conveners: Luis Gimeno, Gonzalo Miguez Macho, Lan Wang-ErlandssonECSECS, Fernando JaramilloECSECS
vPICO presentations
| Wed, 28 Apr, 09:00–10:30 (CEST)

Session assets

Session materials

vPICO presentations: Wed, 28 Apr

Chairpersons: Ruud van der Ent, Fernando Jaramillo, Lan Wang-Erlandsson
09:00–09:05
Land surface feedbacks on the atmospheric water cycle
09:05–09:07
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EGU21-6204
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ECS
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Highlight
Marianne Pietschnig, Abigail L. S. Swann, Ruth Geen, F. Hugo Lambert, and Geoffrey K. Vallis

Projected precipitation changes over tropical land tend to be enhanced by vegetation responses to CO2 forcing in Earth System Models. Projected decreases in rainfall over the Amazon basin and increases over the Maritime Continent are both stronger when plant physiological changes are modelled than if these changes are neglected, but the reasons for this amplification remain unclear. The responses of vegetation to increasing CO2 levels are complex and uncertain, but changes in stomatal conductance likely dominate the evapotranspiration response in Earth System Models.

We investigate why vegetation changes cause precipitation to increase more strongly over the Maritime Continent while decreasing more strongly over the Amazon basin. We employ an idealized Atmospheric General Circulation Model with a simplified vegetation scheme that captures CO2-driven stomatal closure.

We find that – counter-intuitively – rainfall is enhanced over a narrow rectangular island when terrestrial evaporation falls to zero with high CO2. Strong heating and ascent over the island trigger moisture advection from the surrounding ocean. In contrast, over larger continents rainfall depends on continental moisture recycling.

Simulations with two large rectangular continents representing South America and Africa reveal that the stronger decrease in rainfall over the Amazon basin is due to a combination of local and remote effects:

Finally, we investigate the impact of land-surface hydrology on continental rainfall on seasonal timescales. Using our idealized model and realistic continents, we study the strength of the South East Asian monsoon for different continental evaporation schemes. Surprisingly, when terrestrial evapotranspiration is unlimited (i.e. does not depend on soil moisture availability), monsoon precipitation is much weaker than when terrestrial evapotranspiration is limited by soil moisture. In order to explain this behavior, we compare the atmospheric energy budgets and circulation between the simulations.

Our results show that the land-surface hydrology plays an important role in modifying tropical precipitation and atmospheric dynamics on seasonal timescales and in the long-term under climate change, and that further investigation into the topic is called for.

How to cite: Pietschnig, M., Swann, A. L. S., Geen, R., Lambert, F. H., and Vallis, G. K.: Exploring the effects of the land surface on tropical precipitation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6204, https://doi.org/10.5194/egusphere-egu21-6204, 2021.

09:07–09:09
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EGU21-2281
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ECS
Tat Fan Cheng, Mengqian Lu, and Lun Dai

As the world population continues to rise under global warming, it becomes increasingly urgent to understand the climate system and atmospheric water cycle,  which could be beneficial for assessing future freshwater resources and land-use management. Recent endeavors by the regional studies were put to identify the source-receptor network and synoptic-scale moisture transport in major river basins worldwide affected by monsoons. Notably, growing studies suggest the transboundary upwind moisture sources are, in fact, very crucial to the intensity and variability of precipitation in the downwind areas, which arouses the call for international governance over land-use and water management. Recognizing the need for international governance on moisture sources from different regional studies and considering results from many moisture-sink-orientated studies, it, however, remains largely unclear where exactly are the moisture source hotspots that are shared by most countries and societies. Such information would better facilitate the international attention, effort and policymaking to safeguard those influential moisture hotspots. Further, more scientific questions need to be addressed: how these global moisture hotspots vary in time and space for the past few decades, and how would these changes be attributed to the known climate events and even human activities.

To these ends, we utilize a state-of-the-art three-dimensional Lagrangian model, the FLEXible PARTicle dispersion model (FLEXPART), to homogeneously divide the atmosphere into six million parcels with roughly equal masses and simulate their movements from 1971 to 2010. Instead of focusing on a particular sink region, all the moisture released over land is backtracked to construct a map of moisture hotspots throughout seasons. As surprising as it may seem, the results suggest the majority of global moisture source hotspots for land precipitation are also terrestrial, especially those located in the Amazon rainforest, the Congo rainforest, the Ganges river basin, the Mekong river basin and the Yangtze River basin. Most of these hotspots also situate in monsoonal domains where their strengths vary significantly across seasons. Given also significant interannual variabilities and long-term trends in the strength of these globally shared moisture hotspots, we suspect that climatic events, global warming and urbanization processes could be attributable to the changes in the hotspots. Findings from this work would advance our knowledge of the location of global moisture hotspots that are key to the precipitation over land. Understanding the possible linkages between the hotspots’ changes and climatic events and human-related activities could benefit long-term planning of regional and international strategies for securing freshwater resources.

How to cite: Cheng, T. F., Lu, M., and Dai, L.: Global moisture hotspots for terrestrial precipitation: the variabilities and possible linkages to climatic events and human activities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2281, https://doi.org/10.5194/egusphere-egu21-2281, 2021.

09:09–09:11
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EGU21-5810
Iva Hunova, Marek Brabec, Marek Malý, Alexandru Dumitrescu, and Jan Geletič

Fog is a very complex phenomenon (Gultepe et al., 2007). In some areas it can contribute substantially to hydrological and chemical inputs and is therefore of high environmental relevance (Blas et al., 2010). Fog formation is affected by numerous factors, such as meteorology, air pollution, terrain (geomorphology), and land-use.

In our earlier studies we addressed the role of meteorology and air pollution on fog occurrence (Hůnová et al., 2018) and long-term trends in fog occurrence in Central Europe (Hůnová et al., 2020). This study builds on earlier model identification of year-to-year and seasonal components in fog occurrence and brings an analysis of the deformation of the above components due to the individual explanatory variables. The aim of this study was to indicate the geographical and environmental factors affecting the fog occurrence.

       We have examined the data on fog occurrence from 56 meteorological stations of various types from Romania reflecting different environments and geographical areas. We used long-term records from the 1981–2017 period. 

       We considered both the individual explanatory variables and their interactions. With respect to geographical factors, we accounted for the altitude and landform. With respect to environmental factors,   we accounted for proximity of large water bodies, and proximity of forests. Geographical data from Copernicus pan-European (e.g. CORINE land cover, high resolution layers) and local (e.g. Urban Atlas) projects were used. Elevation data from EU-DEM v1.1 were source for morphometric analysis (Copernicus, 2020).

        We applied a generalized additive model, GAM (Wood, 2017; Hastie & Tibshirani, 1990) to address nonlinear trend shapes in a formalized and unified way. In particular, we employed penalized spline approach with cross-validated penalty coefficient estimation. To explore possible deformations of annual and seasonal components with various covariates of interest, we used (penalized) tensor product splines to model (two-way) interactions parsimoniously, Wood (2006).

       The fog occurrence showed significant decrease over the period under review. In general the selected explanatory variables significantly affected the fog occurrence and their effect was non-linear. Our results indicated that, the geographical and environmental variables affected primarily the seasonal component of the model. Of the factors which were accounted for, it was mainly the altitude showing the clear effect on seasonal component deformation (Hůnová et al., in press).

      

 

References:

Blas, M, Polkowska, Z., Sobik, M., et al. (2010). Atmos. Res. 95, 455–469.

Copernicus Land Monitoring Service (2020). Accessed online at: https://land.copernicus.eu/.

Gultepe, I., Tardif, R., Michaelidis, S.C., Cermak, J., Bott, A. et al. (2007). Pure Appl Geophys, 164, 1121-1159.

Hastie, T.J., Tibshirani, R.J. (1990). Generalized Additive Models. Boca Raton, Chapman & Hall/CRC.

Hůnová, I., Brabec, M., Malý, M., Dumitrescu, A., Geletič, J. (in press) Sci. Total Environ. 144359.

Hůnová, I., Brabec, M., Malý, M., Valeriánová, A. (2018) Sci. Total Environ. 636, 1490–1499.

Hůnová, I., Brabec, M., Malý, M., Valeriánová, A. (2020) Sci. Total Environ. 711, 135018.

Wood, S.N. (2006) Low rank scale invariant tensor product smooths for generalized additive mixed models. Biometrics 62(4):1025-1036

Wood, S.N. (2017). Generalized Additive Models: An Introduction with R (2nd ed). Boca Raton, Chapman & Hall/CRC.

 

How to cite: Hunova, I., Brabec, M., Malý, M., Dumitrescu, A., and Geletič, J.: Environmental and geographical effects on fog occurrence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5810, https://doi.org/10.5194/egusphere-egu21-5810, 2021.

09:11–09:13
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EGU21-8984
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ECS
Eli Dennis and Ernesto Berbery

Soil hydrophysical properties are necessary components in weather and climate simulation; yet, the parameter inaccuracies may introduce considerable uncertainty in the representation of surface water and energy fluxes. The surface fluxes not only affect the terrestrial water and energy budgets, but through land-atmosphere interactions, they can influence the boundary layer, atmospheric stability, moisture transports, and regional precipitation characteristics. This study uses seasonal coupled simulations to examine the uncertainties in the North American atmospheric water cycle that result from the use of different soil datasets. Two soil datasets are considered: State Soil Geographic dataset (STATSGO) from the United States Department of Agriculture and Global Soil Dataset for Earth System Modeling (GSDE) from Beijing Normal University.  Each dataset's dominant soil category allocations differ significantly at the model's resolution (15 km). It is found that large coherent regional discrepancies exist in the assignments of soil category, such that, for instance, in the Midwestern United States (hereafter, Midwest), there is a systematic reduction in soil grain size. Because the soil grain size is regionally biased, it allows for analysis of the impact of soil hydrophysical properties projected onto regional scales.

The two simulations are conducted from June 1–August 31, 2016–2018 using the Weather Research and Forecasting Model (WRF) coupled with the Community Land Model (CLM) version 4. It is found that in the Midwest, where the soil grain size decreases from STATSGO to GSDE, the GSDE simulation experiences reduced mean latent heat flux (–15 W m-2), and increased sensible heat flux (+15 W m-2).  The differences in fluxes lead to differences in low-level specific humidity and 2-m temperature. The boundary layer thermodynamic structure responds to these changes resulting in differences in mean CAPE and CIN. In the GSDE simulation, there is more energy available for convection (CAPE: +200 J kg-1) in the Midwest, but it is more difficult to access that energy (CIN: +75 J kg-1). Furthermore, a reduction in low-level moisture generates a similar reduction in column-integrated moisture (i.e., precipitable water), resulting in conditions that are less conducive for precipitation.

Interestingly, the soil-texture-related surface fluxes are not confined to thermodynamic influence, but their influence extends to dynamic fields as well. Differences in the vertically-integrated wind field suggest a weakening of the continental low-pressure system (i.e., denoted by a reduction in cyclonic rotation) co-located with the decrease in latent heat flux in the Midwest. The associated vertically-integrated moisture fluxes mirror the dissimilarities in the wind fields. Consequently, the moisture fluxes yield differences in vertically-integrated moisture flux convergence in the same region, as well. This combination of thermodynamic and dynamic variable differences culminates in a reduction of average precipitation in the Midwest, which can be related to changes in the placement of soil hydrophysical properties via soil texture. Through land-atmosphere interactions, it is shown that soil parameters can affect each component of the atmospheric water budget.

How to cite: Dennis, E. and Berbery, E.: The role of soil hydrophysical properties in the atmospheric water cycle, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8984, https://doi.org/10.5194/egusphere-egu21-8984, 2021.

09:13–09:15
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EGU21-10860
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ECS
Stefano Natali, Giovanni Zanchetta, Ilaria Baneschi, Marco Doveri, and Roberto Giannecchini

Stable water isotopes of precipitation are widely used to track processes occurring within the hydrological cycle and to understand regional atmospheric patterns that influence a specific area. Moreover, the use of the oxygen isotopic composition in continental carbonates (e.g. speleothems) is a well-established practice to reconstruct climatic variations in the recent past. In the Mediterranean basin, the continental carbonate δ18O is generally used as a proxy of paleo-precipitation since the water-calcite fractionation factor is able to compensate the δ18O-T gradient of about 0.2‰/°C typical of rainfall in this area. However, few comprehensive investigations were performed in the Western Mediterranean in order to analyze the statistical relationships between measured stable isotopes in precipitation and meteorological variables, and none of them accounted for the possible seasonality in these relationships. Understanding the degree of dependence of the rainfall isotopic signature from precipitation amount and temperature at present day is of primary importance in Tuscany (Central-Western Italy), where many performed palaeohydrological studies require a more precise and quantitative interpretation. To this end, in the present study 560 isotope monthly data (δ18O, δ2H, and deuterium excess) of precipitation collected in 11 sites through Tuscany from 1971 to 2018 were gathered in a database. A large part of dataset was extracted from GNIP database (and integrated with new data) or derived from local hydrogeological studies, whereas 83 new measurements were produced at two novel sites. Then, only sites whose monthly data covered almost one year were considered for processing, resulting in 474 precipitation samples archived along with monthly mean temperature and rainfall amount. In this framework, a LMWL for Tuscany Region was determined for the first time by applying different regression techniques. A Spearman’s rank correlation analysis was performed to summarize the strength and direction of the relationship between stable isotope signatures of precipitation and meteorological variables, both at monthly and annual timescale. The monthly correlation was also investigated on seasonal basis. Finally, the influence of local geographical effects (altitude, distance to the coast, etc.) on the isotopic signals registered at different sites was evaluated.

How to cite: Natali, S., Zanchetta, G., Baneschi, I., Doveri, M., and Giannecchini, R.: Meteorological and geographical control on stable isotope signature of precipitation in a Western Mediterranean area (Tuscany, Central Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10860, https://doi.org/10.5194/egusphere-egu21-10860, 2021.

09:15–09:17
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EGU21-15579
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ECS
Cristina Passet, Lan Wang-Erlandsson, Yoshihide Wada, Agnes Pranindita, and Agatha De Boer
A substantial portion of groundwater abstracted from aquifers is used for irrigation and evaporated to the atmosphere, potentially contributing towards downwind precipitation. While the fate of evaporation fluxes from land have been analysed, the atmospheric pathways of evaporation originating from groundwater have not yet been globally quantified. This study analysed the geographical distribution, the seasonality and the magnitude of groundwater-dependent precipitation (Pgw) at a global scale and for a selection of countries and river basins. The Eulerian moisture tracking WAM-2layers model was used to process meteorological and groundwater abstraction input data from 1980 to 2010.  Results show considerable contributions of groundwater to precipitation downwind of the most heavily irrigated areas, leading to net groundwater losses over these areas. Globally, 40% of the Pgw precipitates directly in the oceans, and do not contribute to biomass production in terrestrial ecosystems. Some of the countries with the highest rates of groundwater abstraction (India, the USA, Pakistan and Iran), receive low volumes of Pgw and are net losers of groundwater resources. The countries with the highest net gain of groundwater are China, Canada and Russia. At river basin scale, the Indus, Ganges and Mississippi basins are net losers of groundwater to downwind Pgw, while the Yangtze, Tarim and Brahmaputra basins receive more Pgw than their groundwater withdrawals. The share of precipitation that originates from groundwater varies considerably with seasons, and can be especially high when low local precipitation levels occur in combination with high upwind groundwater abstraction. Furthermore, precipitation dependence on groundwater (ρgw), has steadily increased between 1980 to 2010 in all studied areas and globally. Our study suggests that the countries and basins with a high and increasing dependency on ρgw to support their precipitation can be vulnerable to groundwater availability upwind.

How to cite: Passet, C., Wang-Erlandsson, L., Wada, Y., Pranindita, A., and De Boer, A.: The spatio-temporal evolution of groundwater dependent precipitation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15579, https://doi.org/10.5194/egusphere-egu21-15579, 2021.

Land-use and climate change effects on the atmospheric water cycle
09:17–09:19
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EGU21-675
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ECS
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Highlight
Amen Al-Yaari, Agnes Ducharne, Wim Thiery, Frederique Cheruy, and David Lawrence

Irrigated areas have increased, faster than the growth of the world population, from around 0.63 million km2 at the start of the 20th century to 3.1 million km2 of land in 2005, that is five times of area in 1900 (0.6 million km2). Irrigation is one of the land management practices with the largest biogeochemical and biogeophysical effects on climate. However, incorporating land management factors (including irrigation) into most of the state‐of‐the‐art climate models under the Coupled Model Intercomparison Project, Phase 6 (CMIP6) coordinated by the World Climate Research Programme (WCRP) is still overlooked. To our best knowledge, three models, however, take into account irrigation activities: namely NorESM2‐LM, GISS‐E2‐H, and CESM2. The overall objective of the study is to investigate the role of irrigation on climate change at the global scale by looking at temporal trends of Essential Climate variables (ECVs) that characterize the Earth's climate (Evapotranspiration, leaf area index, precipitation, soil moisture, radiation, and air temperature) over the last 115 years (i.e. 1900-2014). Within this investigation, we compared models with irrigation vs. models without irrigation using 20 models from different CMIP6 experiments: coupled land-atmosphere amip (observed sea surface temperatures and sea ice concentrations), coupled land-atmosphere-ocean historical simulation, and offline land-hist (land only simulations). Temporal trends over the 1900-2014 period were computed then spatially binned by the "FAO Global Map of Irrigation Areas", which represents area equipped for irrigation expressed as percentage of total area around the year 2005. For the three CMIP6 experiments, the three models with irrigation switched on showed similar and distinguished behavior from all other models with irrigation switched off over intensively irrigated areas: mean annual evapotranspiration and soil moisture increased over time (positive trends vs. negative or no trends for all other none-irrigation models). This increase in evapotranspiration over time was reflected in the negative trends (i.e. cooling) of annual maximum air temperature for the irrigation models vs. positive trends for most of the none-irrigation models. The ET temporal positive trends over intensively irrigated areas were detected and confirmed by four different satellite-based ET products. The consistent results among the three experiments and confirmed by different satellite data imply the importance of incorporating anthropogenic factors in the next generation of climate models.

How to cite: Al-Yaari, A., Ducharne, A., Thiery, W., Cheruy, F., and Lawrence, D.: The role of irrigation expansion on historical climate change during the last 115 years: insights from CMIP6, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-675, https://doi.org/10.5194/egusphere-egu21-675, 2021.

09:19–09:21
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EGU21-7697
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ECS
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Highlight
Anne J. Hoek van Dijke, Imme Benedict, Kaniska Mallick, Martin Herold, Miriam Machwitz, Martin Schlerf, and Adriaan J. Teuling

Vegetation plays an important role in the exchange of water between the land surface and the atmosphere through evaporation and redistribution of water. Hence, changes in vegetation cover alter the terrestrial hydrological cycle. Large-scale forest restoration is an effective climate change mitigation strategy through carbon sequestration and is expected to impact the water availability. A better understanding of the impact of reforestation is needed, given the numerous different reforestation missions.

Our study aims to provide an estimation of the hydrological effects of 900 million hectares of reforestation, called the ‘global tree restoration potential’ (Bastin et al., 2019). We include the effects of forest planting on evaporation and moisture recycling, where evaporation effects local water availability, and moisture recycling effects both local and remote water availability. We used the conventional Budyko’s moisture index framework to calculate the effects of reforestation on evaporation, and afterwards we used the UTrack dataset to calculate the changes in precipitation. The UTrack dataset presents the monthly climatological mean atmospheric moisture flows from evaporation to precipitation and is created using the Lagrangian moisture tracking model UTrack (Tuinenburg et al., 2020).

The results show that reforesting the ‘global tree restoration potential’ would effect water availability for most of the Earth’s surface. The global mean increase in terrestrial evaporation is 8 mm yr-1. The increase in evaporation is highest around the equator (on average 20 mm yr-1), with local maximum changes of up to 200 mm yr-1. This is related to a relatively high restoration potential in low latitude areas, and a generally large evaporation response in high precipitation regions. Enhanced moisture recycling has the potential to partly compensate for this decreased water availability by increasing the downwind precipitation.

 

Bastin, J.-F., Finegold, Y., Garcia, C., Mollicone, D., Rezende, M., Routh, D., Zohner, C.M., Crowther, T.W. The global tree restoration potential. Science, 365, 76-79, http://doi.org/10.1126/science.aax0848, 2019.

Tuinenburg, O. A., Theeuwen, J. J. E., and Staal, A.: High-resolution global atmospheric moisture connections from evaporation to precipitation, Earth Syst. Sci. Data, 12, 3177–3188, https://doi.org/10.5194/essd-12-3177-2020, 2020.

How to cite: Hoek van Dijke, A. J., Benedict, I., Mallick, K., Herold, M., Machwitz, M., Schlerf, M., and Teuling, A. J.: The ‘global tree restoration potential’: a first estimation of the hydrological effects, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7697, https://doi.org/10.5194/egusphere-egu21-7697, 2021.

09:21–09:23
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EGU21-9251
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ECS
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Highlight
Juan Sierra, Jhan Carlo Espinoza, Clementine Junquas, Jan Polcher, Miguel Saavedra, Jorge Alcides Molina Carpio, Marcos Andrade, Thomas Condom, and Laura Ticona

The Amazon rainforest is a key component of the climate system and one of the main planetary evapotranspiration sources. Over the entire Amazon basin, strong land-atmosphere feedbacks cause almost one third of the regional rainfall to be transpired by the local rainforest. Maximum precipitation recycling ratio takes place on the southwestern edge of the Amazon basin (a.k.a. Amazon-Andes transition region), an area recognized as the rainiest and biologically richest of the whole watershed. Here, high precipitation rates lead to large values of runoff per unit area providing most of the sediment load to Amazon rivers. As a consequence, the transition region can potentially be very sensitive to Amazonian forest loss. In fact, recent acceleration in deforestation rates has been reported over tropical South America. These sustained land-cover changes can alter the regional water and energy balances, as well as the regional circulation and rainfall patterns. In this sense, the use of regional climate models can help to understand the possible impacts of deforestation on the Amazon-Andes zone.

This work aims to assess the projected Amazonian deforestation effects on the moisture transport and rainfall behavior over tropical South America and the Amazon-Andes transition region. We perform 10-year austral summer simulations with the Weather Research and Forecasting model (WRF) using 3 one-way nested domains. Our finest domain is located over the south-western part of the basin, comprising two instrumented Andean Valleys (Zongo and Coroico river Valleys). Convective permitting high horizontal resolution (1km) is used over this domain. The outcomes presented here enhance the understanding of biosphere-atmosphere coupling and its deforestation induced disturbances.

How to cite: Sierra, J., Espinoza, J. C., Junquas, C., Polcher, J., Saavedra, M., Molina Carpio, J. A., Andrade, M., Condom, T., and Ticona, L.: Deforestation impacts on Amazon-Andes hydroclimatic connectivity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9251, https://doi.org/10.5194/egusphere-egu21-9251, 2021.

09:23–09:25
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EGU21-7017
Craig R. Ferguson

In the semi-arid U.S. Great Plains, nocturnal southerly low-level jets (LLJs) serve critical roles as conveyors of remotely-sourced (i.e., Gulf of Mexico) water vapor and agents of atmospheric instability in the warm-season.  Defined by a diurnally oscillating wind maximum between 0–3 km above the surface, LLJs have been studied by meteorologists for over 60-years due to their role in severe weather outbreaks. It is only within the past decade that a subset of LLJs with especially high vertically integrated water vapor transport, termed atmospheric rivers, have drawn the attention of hydrologists.

In this study, changes in LLJ frequency and structure over the period from 1901–2010 are quantified using ECMWF’s Coupled Reanalysis of the Twentieth Century (CERA-20C). A new objective dynamical LLJ classification dataset is used to separately quantify changes in the two predominant LLJ types: synoptically coupled and uncoupled. The findings reveal that both the frequency of Great Plains LLJs and their associated precipitation have decreased significantly over the 20th century. Decreases in LLJ associated precipitation range between 10–14% of total present day May–September precipitation. The largest differences observed are attributable to uncoupled jet frequency and structural changes during July and August over the central and northern Great Plains. Overall, the results indicate the contribution of LLJs to the region’s water budget has diminished.

How to cite: Ferguson, C. R.: The diminishing contribution of low-level jets to the U.S. Great Plains water budget, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7017, https://doi.org/10.5194/egusphere-egu21-7017, 2021.

General feedback processes in the atmospheric water cycle and extremes
09:25–09:27
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EGU21-12386
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ECS
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Highlight
Rogert Sorí, Raquel Nieto, Margarida L.R. Liberato, and Luis Gimeno

The regional and global precipitation pattern is highly modulated by the influence of El Niño Southern Oscillation (ENSO), which is considered the most important mode of climate variability on the planet. In this study was investigated the asymmetry of the continental precipitation anomalies during El Niño and La Niña. To do it, a Lagrangian approach already validated was used to determine the proportion of the total Lagrangian precipitation that is of oceanic and terrestrial origin. During both, El Niño and La Niña, the Lagrangian precipitation in regions such as the northeast of South America, the east and west coast of North America, Europe, the south of West Africa, Southeast Asia, and Oceania is generally determined by the oceanic component of the precipitation, while that from terrestrial origin provides a major percentage of the average Lagrangian precipitation towards the interior of the continents. The role of the moisture contribution to precipitation from terrestrial and oceanic origin was evaluated in regions with statistically significant precipitation anomalies during El Niño and La Niña. Two-phase asymmetric behavior of the precipitation was found in regions such the northeast of South America, South Africa, the north of Mexico, and southeast of the United States, etc. principally for December-January-February and June-July-August. For some of these regions was also calculated the anomalies of the precipitation from other datasets to confirm the changes. Besides, for these regions was calculated the anomaly of the Lagrangian precipitation, which agrees in all the cases with the precipitation change. For these regions, it was determined which component of the Lagrangian precipitation, whether oceanic or terrestrial, controlled the precipitation anomalies. A schematic figure represents the extent of the most important seasonal oceanic and terrestrial sources for each subregion during El Niño and La Niña.

How to cite: Sorí, R., Nieto, R., Liberato, M. L. R., and Gimeno, L.: Anomalies of continental precipitation associated with El Niño Southern Oscillation: the role of moisture contribution from oceanic and terrestrial sources , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12386, https://doi.org/10.5194/egusphere-egu21-12386, 2021.

09:27–09:29
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EGU21-2082
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ECS
Helene Brogniez, Jia He, Laurence Picon, Marc Schroder, René Preusker, and Olaf Danne

Water vapor is one of the fundamental elements in the atmosphere. Its distribution is strongly associated with large-scale atmospheric circulation. Here the new global water vapor climate data records (CDR) generated within the ESA Water Vapor CCI+ project (WV_cci) is used to perform a comprehensive evaluation of total column water vapor provided by 21 global climate models (CMIP6 framework). The ESA WV_cci CDRs cover the period 2002-2017 with a daily frequency and a regular 0.5° spatial resolution. The focus is on the tropical region (30°S - 30°N). The observational diagnostic relies on the decomposition of the tropical atmosphere into large-scale dynamical regimes using the 500 hPa atmospheric vertical velocity w500 (in hPa/day) as a proxy. The ESA WV_cci and the CMIP6 data are then sorted according to dynamical regimes (intervals of 10 hPa/day) allowing to study the evolution of the regimes in terms of frequency of occurrence and is linked to water vapor variation. While the basic picture of the tropical atmosphere is properly represented by the models (moister in ascending branches, drier in subsiding branches) there are noticeable differences in the patterns that will be discussed. The inter-annual variation of water vapor for both observation and the models will be analyzed, and the trend significance are assessed using Mann-Kendall test. This highlights the interest of water vapor climate data records for model evaluation.

How to cite: Brogniez, H., He, J., Picon, L., Schroder, M., Preusker, R., and Danne, O.: Evaluation of the tropical water vapor of CMIP6 GCMs with ESA CCI+ “Water Vapor” climate data records: Insights from large-scale atmospheric circulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2082, https://doi.org/10.5194/egusphere-egu21-2082, 2021.

09:29–09:31
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EGU21-7902
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ECS
Sarosh Alam Ghausi, Axel Kleidon, and Subimal Ghosh

Extreme precipitation is expected to increase at the rate of 7% per degree rise in temperature as suggested by the Clausius-Clapeyron equation (also known as CC scaling). Observations however, show deviations from the CC rate, with mostly negative precipitation - temperature scaling in warm tropical regions. Here we explain the negative precipitation scaling in the tropics with the cloud radiative effect on surface temperatures. Temperatures are shaped by the surface energy balance, which is affected by clouds, and hence temperatures are not independent of precipitation. We used observations from India and found negative scaling rates over most regions as extreme precipitation scaling tends to breakdown at temperatures of about 23◦to 25◦C. We show that these negative scaling rates arise from the radiative cooling of clouds associated with precipitation events which is predominant in India during the summer monsoon season. To test our hypothesis, we used an energy balance model constrained by assumption that convective exchange within atmosphere works at its thermodynamic limit of maximum power. Using the NASA-CERES radiation product, we calculated surface temperatures for “All sky” and “Clear sky” conditions to include/exclude the effect of cloud radiative forcing. Our results show a diametric change in precipitation scaling after removing the cooling effect of clouds on surface temperatures. Negative precipitation scaling (-4% /◦C) was found when using “All sky” conditions, but these come close to the CC rate (7% to 9% /◦C) when estimated using temperatures derived from “Clear sky” conditions. The breakdown in extreme precipitation scaling at high temperatures also disappeared forthe “Clear sky” temperatures. This implies that the breakdown in scaling may not relate to changes in aridity or the lack of moisture, but rather to the associated changes in cloud cover. Negative scaling rates derived from observations are thus likely to misrepresent the response of extreme precipitation to global warming in tropical regions. Our findings suggest that an intensification of precipitation extremes at CC rate with global warming is consistent with observations.

Keywords: Extreme Precipitation, CC scaling, Maximum Power, Indian Mon-soon

How to cite: Ghausi, S. A., Kleidon, A., and Ghosh, S.: Attributing the negative scaling of extreme precipitation with temperature over India to cloud radiative cooling during the monsoon season, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7902, https://doi.org/10.5194/egusphere-egu21-7902, 2021.

09:31–09:33
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EGU21-9326
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ECS
Marta Vázquez, Raquel Nieto, Margarida Liberato, and Luis Gimeno

The teleconnection patterns are an important feature influencing the variability of moisture transport toward the continent. This work analyses the influence of the Arctic Oscillation, Antarctic Oscillation, Pacific North America, and ENSO on the moisture transport from major oceanic and continental moisture sources in the month of higher precipitation. The Pacific North America higher influence is observed over North America with an increased contribution to the western region from the Pacific and lower over the eastern region from the Atlantic in the positive phase. The moisture transport during Arctic Oscillation events seems to be modulated by the Mediterranean Sea and North Atlantic, increasing from the Mediterranean in the positive phase and decreasing from the Atlantic. The Antarctic Oscillation shows its most relevant influence over Australia and Eastern Africa, with increased moisture contribution from eastern regions on the positive phase. Finally, ENSO events show influence in moisture transport over different areas in the world. El Niño events are associated with increased transport from the Atlantic region over western Europe and from the Pacific over North America. In South and Central America, the moisture contribution decreased over the regions closer to the equator, while the opposite occurs over southern South America. Over eastern Africa and Southern Asia, moisture inflow from the Indian Ocean seems to be affected by the pattern. The result suggests the influence of the moisture contribution on the precipitation pattern in association with main teleconnection patterns.

How to cite: Vázquez, M., Nieto, R., Liberato, M., and Gimeno, L.: Global moisture transport and the role of major teleconnection patterns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9326, https://doi.org/10.5194/egusphere-egu21-9326, 2021.

09:33–09:35
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EGU21-13586
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ECS
Milica Stojanovic, Ana Gonçalves, Rogert Sorí, Marta Vázquez, and Margarida L.R. Liberato

Three consecutive extratropical cyclones named Daniel, Elsa, and Fabien affected the northwest of the Iberian Peninsula during December 2019. In this region is located the Miño-Limia-Sil Hydrographic Demarcation (MLSHD), which includes part of Galicia, in Spain and the north of Portugal. The water resources of the MLSHD are of great importance for the socio-economic framework of both countries, particularly for the agricultural and livestock activities, tourism, and the production of electrical energy from renewable sources like the eolic and the hydroelectric. In this study was analysed the synoptic characteristics of these extratropical cyclones, particularly during the life cycle close to the Iberian Peninsula, when the greatest damages associated with strong winds and intense rainfall occurred. The storm Daniel was formed from a secondary low located to the west and close to the Iberian Peninsula during the afternoon of December 15. Nevertheless, Elsa was formed in the Gulf of Mexico and Fabian in the north Atlantic Ocean, then both crossed the north Atlantic Ocean to finally affect with intense rainfall that caused floods in the MLSHD from 18 to 21 December 2019. The moisture supplies from the tropical north Atlantic Ocean, revealed by the integrated water vapour transport favoured the intensification of all these systems. The consecutive impact of these systems provided great amounts of rainfall to the MLSHD, causing positive anomalies of the total accumulated rainfall for this month. An assessment of drought conditions through the SPI and the SPEI on time scales of 1, 3, 6, and 12 months exposed the role of these systems on drought busting in the MLSHD. Therefore, despite the negative impacts, these systems favoured a recovery of the hydrological conditions of the Demarcation. Our results confirm the importance of studying for a long study period the role of extratropical cyclones on hydrological conditions of the MLSHD.

Acknowledgements:
This study is supported by Fundação para a Ciência e a Tecnologia, Portugal (FCT), under project WEx-Atlantic (PTDC/CTA-MET/29233/2017).

How to cite: Stojanovic, M., Gonçalves, A., Sorí, R., Vázquez, M., and Liberato, M. L. R.: The role of consecutive extratropical cyclones Daniel, Elsa, and Fabien on drought busting during December 2019 in the Minho-Limia-Sil Hydrographic demarcation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13586, https://doi.org/10.5194/egusphere-egu21-13586, 2021.

09:35–10:30