The Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) when combined with traditional data sources (geochronology, geochemistry, hydrology, modelling) can enhance our understanding and monitoring of elements of hydrologic systems including recharge of reservoirs, groundwater flow direction and rates, and the impacts of climate change on watersheds worldwide.  We cite a few examples. Large seasonal fluctuations (peak: Nov./Dec.; trough: July/Aug.) in Lake Nasser's surface water levels are accompanied by an increase in GRACE_TWS (average: 50 ± 13 mm/yr, up to 77 ± 18 mm/yr) over Lake Nasser in Upper Egypt and by a progression of a front of increasing GRACE_TWS values (> 50 ± 13 mm) away from the lake reaching distances of up to 700 km some 3 to 5 months following peak lake level periods. Those patterns are consistent with rapid turbulent groundwater flow from Lake Nasser along preferred flow directions (networks of faults and karst topography). The Tigris Euphrates watershed (30 dams) showed an impressive recovery following a prolonged drought (2007–2018; Average Annual Precipitation [AAP]: ~400 km³) by an extreme precipitation event in 2019 (726 km³) with no parallels in the past 100 years. This recovery (113±11 km³) compensated for 50% of the losses endured during drought by impounding a large portion of the runoff within the reservoirs (capacity: 250 km³). The Aswan High Dam, with its storage capacity of 150 km³ represents one of the best-engineered systems that enabled Egypt to ride out droughts and avoid extreme flooding events that affected neighboring Sudan. Additional engineering structures are recommended to take advantage of the excess Lake Nasser waters (35 km³), now residing in the Tushka lakes. In basins lacking artificial reservoirs, a different response to extreme precipitation events is observed from temporal GRACE solutions. Extreme precipitation events (2011-2022) over northern Arabia (PPT: Hail: 8.43 km³; Ad-Dahna: 2.22 km³ and Medina: 3.71 km³) and central Arabia (PPT: Riyadh: 4.66 km³ and Mecca: 0.21 km³) produced an increase in GRACE_TWS that lasted for a few months only. Cyclones over Oman (2011and 2015; PPT: 6 and 6.6 km³, respectively) had a similar effect. Findings demonstrate that highly engineered watersheds are better prepared to deal with the projected increase in the frequency and intensity of extreme rainfall and drought events in the 21st century.

How to cite: Sultan, M., Abdelmohsen, K., Saleh, H., and Karimi, H.: Recharge from Reservoirs, Groundwater Flow, and Response to Climate Variability in Arid Basins: Revelations from GRACE Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9959, https://doi.org/10.5194/egusphere-egu23-9959, 2023.

Understanding and quantifying hydrology processes represent a mandatory step in semi-arid and arid regions for defining the vulnerability of these environments to climate change and human pressure, as well as for providing useful data to steer mitigation and resilience strategies. This generally valid concept becomes even more stringent for highly sensitive ecosystems, such as small islands.

It is the case of Pianosa Island (Tuscan Archipelago) that extends a few more than 10 km² within the Tyrrhenian Sea and it is characterised by a flat morphology (maximum altitude 29 m a.s.l.) and semi-arid climate conditions (550 mm and 17 °C as mean annual precipitation and temperature).

Because of the morphology and the medium-high permeability of superficial bio-calcarenite rocks, superficial water are absent. Nevertheless, the peculiar geological-hydrogeological setting guarantee a storage of groundwater in a phreatic aquifer and semi-confined/confined system, hitherto able to satisfy the local human water demand, mainly tied to seasonal tourism (thousands of visitors/year) and domestic exigencies (less than 30 permanent people). Evapotranspiration represents the most important voice of the water budget, given the windy and relative high temperature conditions.

In the precarious hydro-equilibrium for biosphere and human communities, and considering sea-level rise and climate regime trends that the Mediterranean is experiencing, HYDRO-ISLAND project (UNESCO’s program) intends to deploy a multi-disciplinary approach (geology, hydrogeology, geochemistry, geophysics, remote sensing-smart technology) for better understanding and quantifying the hydrological processes affecting the water availability and for sharing data and transfer knowledge to the community and younger generations, possibly suggesting best practices for water sustainability.

First results pointed out as over the last decade the annual rainfall weakly tended to increase, but at the same time such increasing resulted concentrated in summer and autumn seasons, whereas during winter and spring a decreasing tendency is even observed. This precipitation regime has led to a major rate of evapotranspiration and minor effective infiltration that caused a decreasing of piezometric level over several years. Quantity and chemical-isotopic features of rainfall and effective infiltration water measured/collected by a raingauge and a high precision lysimeter describe the hydrological processes at soil level and characterize the rate and seasonality of groundwater recharge in an experimental site. Using multispectral data by drone, we are trying to extend the experimental site information to a wider area in order to understand the general behaviour at island scale. Measurements, water sampling and analyses for shallow and deep wells, together with the study of geological constraints, are highlighting the distribution and relationship among different groundwater components, including the seawater that intrudes the aquifer from the SE side of the island. Furthermore, the comparative analyses of continuative data monitoring in wells and weather station showed the presence of possible concentrated water infiltration processes during rainfall extreme events that induce a quick response of groundwater systems in terms of water level rise and decrease of electrical conductivity. Thus, elements of vulnerability of the aquifer to pollution are pointed out, as well as the possibility to provide technical solutions for enhancing water infiltration and groundwater availability.             

How to cite: Doveri, M., Menichini, M., Foresi, L., Berton, A., Costanza, L., Baneschi, I., Da Prato, S., Milaneschi, L., Raco, B., Santilano, A., Trifirò, S., Giannecchini, R., and Burlando, M.: Hydrological processes in the semi-arid small island of Pianosa: a multidisciplinary approach to increase knowledge, awareness and education on a highly climate-sensitive environment (HYDRO-ISLAND project UNESCO’s program), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15835, https://doi.org/10.5194/egusphere-egu23-15835, 2023.

The Groundwater-Surface water (GW-SW) interaction governed by vertical connectivity, drainage pattern, subsurface lithology, vegetation cover, and land use determines the water availability in semi-arid dryland regions. It plays a crucial role in eco-hydrology, effective water resource management and overall socio-economic development in these marginal environments. Furthermore, the perennial dryland rivers flowing through these semi-arid dryland regions undergo substantial precipitation and flow variability, thus making sustainable water management challenging. Nevertheless, an understanding of the GW-SW dynamics, its spatial variability and the processes influencing the water supply in the semi-arid perennial dryland rivers are still lacking. For this purpose, the stable isotopes of oxygen and hydrogen, in terms of δ¹⁸O, δ²H and d-excess parameters of water samples, have been used to assess the GW-SW interaction in the semi-arid perennial Mahi River basin, India. The Mahi River has a length of ~560 km and a drainage basin area of ~34k km². In total, 53 samples of groundwater and 14 samples of river water were collected during the dry season. In a given river transect, GW samples were collected from both river banks at a distance of around 1 km and 2km, respectively. The result shows changes in GW-SW connectivity at the reach scale. The SW in the downstream and middle reaches (36 to 208km from the river mouth) is characterised by a progressive decrease in δ¹⁸O from -1.3 ‰ to -2.6‰. The decrease in the δ¹⁸O value in the middle and downstream reaches indicates the mixing of depleted GW into the river. The trend changes in the upstream reaches (208 to 491km), where the SW becomes progressively enriched in δ¹⁸O from about -2.1‰ to 0.08‰, with reach scale variability. The upstream reaches also show a decrease in d-excess value from -3.2‰ to -7.2‰, along with the increasing δ¹⁸O values suggesting enhanced evaporation of SW during the low flow conditions. The average δ¹⁸O of SW in the middle and downstream reach is -1.9 ‰, whereas the average δ¹⁸O of the upstream reach is -0.5 ‰. The slope of the GW δ¹⁸O-δ²H regression line is lower than that of the Global Meteoric Water Line (GMWL), suggesting that the GW undergoes substantial evaporation. The variability of isotopic values and mixing of GW with SW demonstrates that the river channel shows enhanced vertical connectivity for middle and downstream reaches even during the dry season. However, there is vertical disconnectivity in the upstream reaches. This study highlights the need for different management strategies for various reaches of the spatially variable and dynamic perennial dryland rivers in a semi-arid region.

How to cite: Raj, A., Jain, V., Bind, V. K., Padhya, V., and Deshpande, R. D.: The GW-SW dynamics of a perennial dryland river in the semi-arid region, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12017, https://doi.org/10.5194/egusphere-egu23-12017, 2023.

Syria is now witnessing the dramatic effects of a multiyear drought that has been afflicting the country since 2006. The drought has impacted several regions, but the north-eastern Al Jazira region, corresponding to the Middle Euphrates River basin and considered the Syrian “breadbasket”, has been hammered particularly severely.

With this paper we aim at contributing to the knowledge on the consequences of multiyear meteorological drought on food security in the basin of the middle range of the Euphrates River in Syria.

Annual precipitation data were collected from 11 ground meteorological stations for the period 1983–2020 covering an area of 96800km². Data were provided by the Syrian Ministry of Agriculture. In addition, the series of two satellite-based indices, namely Vegetation Condition Index (VCI) and Vegetation Health Index (VHI) were collected to analyse the vegetation responses to the meteorological drivers. These indices were downloaded at a resolution of 4-km for the time range 1983-2020, from the Centre for Satellite Applications and Research (STAR) of the National Oceanic and Atmospheric Administration (NOAA). The crop production data, including yields of cotton, wheat, and maize, were collected at provincial level over the period of 1983–2020 from Syria Statistical Yearbook.

Recent changes in meteorological drought features (e.g., frequency and intensity) throughout Syria for the years 1983–2020 were assessed by means of the Standard Precipitation Index (SPI), to characterize the meteorological draughtiness for the Al-Jazira region.

SPI was computed on a 12-month timeline to account for the delayed effect of rainfall deficiency on crop output. Commonly, agricultural droughts are evaluated using drought indices at these long timeframes (e.g., 18 and 24 months) because these longer timescales reflect the accumulated influence of meteorological drought that might alter soil water content and stream flow. The correlation matrices of the series of SPI, averaged at different time scales to focus on the effect of multiyear drought events, with the series of VCI and VHI, will be presented.

This work is preliminary to the GIS application of simplified Benfratello’s water balance method (Barontini et al., 2021) to assess the proneness to water scarcity and the irrigation deficit of different areas of the basin.

References

Barontini, S., Rapuzzi, C., Peli, M., and Ranzi, R.: A GIS based application of Benfratello's method to estimate the irrigation deficit in a semiarid climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12936, https://doi.org/10.5194/egusphere-egu21-12936, 2021.

How to cite: Mohammad, H., peli, M., and Barontini, S.: The Impact of Meteorological Drought on Vegetation Health in the Middle Euphrates River Basin (Syria), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-780, https://doi.org/10.5194/egusphere-egu23-780, 2023.

Rainfall in arid and semi-arid areas converts faster in the local SPAC system. Deluge in drylands may be an important source of groundwater recharge. We have been conducting a thirty-year observational in the Mu Us sandy land at the northwest China, we use remote sensing imagery to observe changes in the water body area and in situ observations to monitor rainfall infiltration. A total of 30 periods of Landsat remote sensing images were processed using the Google Earth platform to obtain the characteristics of surface water body changes. The results show that there are strong seasonal characteristics in the changes of water bodies area in the Mu Us sandy land, with two peaks in April and August, and the inter-monthly area increases of 44.867 km² (28.60%) and 47.832 km² (28.31%) respectively. 379.770 km² to 275.492 km², a total reduction of 104.278 km² (27.46%). Deep soil as a percentage of annual precipitation of woodland, shrubland, grassland, farmland and bare land were 2.88%, 17.36%, 3.64%, 1.21% and 44.30%, respectively. The change in the water body area in the Mu Us sandy land is mainly influenced by three factors, rainfall, vegetation coverage, and human activities, with a correlation coefficient of 0.57 (α=0.05) between rainfall and water body area. The correlation coefficients were 0.79, 0.79 and 0.86 (α=0.05) for the years 1991-1997, 1998-2005 and 2006-2017, respectively; vegetation coverage and water body area were negatively correlated overall in 30 years. The correlation coefficient was 0.57 (α=0.05), indicating that human activities in the Mu Us sandy land have a greater impact and human activities in the sands should be reduced in order to manage the sands.

How to cite: Cheng, Y., Bai, X., Ma, X., Xin, Z., Feng, W., Yang, W., and Zhou, J.: Response of ecological restoration to rainfall in arid zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17048, https://doi.org/10.5194/egusphere-egu23-17048, 2023.

Despite the riparian state of river Yamuna and local groundwater reserves, Delhi depends on other rivers to fulfil the rising demand for drinking water.  In the last ten years, the water demand has increased by 39% (2006-2016). In this study, we have tried to understand the domestic water supply system by studying the spatiotemporal variation in the stable isotopic composition of tap water. The stable water isotopes are powerful tracers of hydrological processes in natural and human-managed systems. There are three primary sources with distinct stable water isotopic composition River Yamuna, Upper Ganga canal, Munak canal and local groundwater reserves; the glacial-fed Himalayan rivers and canals fulfil around 90% of the water demand. Numerous government-operated treatment plants in Delhi purify the water from one of the above sources and supply it to consumers. We collected the water sample at every stage of the water supply, from the primary source to the sink, such as samples of canal or river water, raw water before treatment, filtered water after treatment, storage reservoirs, groundwater samples and finally, the household tap waters. 

Contrary to the river, canal water’s isotopic composition shows no spatial variation. Also, the isotopic composition of raw water is similar to the filtered water, indicating no significant loss due to evaporation or any other hydrological process. However, the isotopic composition of tap water shows considerable variation and deviation from its source value. In most regions, tap water’s isotopic composition is higher than that of source water. In Delhi, among all the other sources, the isotopic composition of surface water is lower than that of groundwater. Thus, only the mixing of groundwater with surface water before supplying it to households can explain the observed large variation in the isotopic composition of tap water. Furthermore, our observation suggests groundwater extraction for domestic purposes has increased from 2019 to 2021. The demand for domestic water per capita is rising with the increase in the population. However, the production of treated water is almost constant and depends upon the raw water availability. The excess extraction of groundwater fulfils the gap between supply and demand. Our study suggests that the surface water (river and canal water), or the number of treatment plants, is insufficient to meet the rising water demand in Delhi, which has led to the overexploitation of limited groundwater reserves in the past few years. Therefore, besides irrigation, the excessive groundwater extraction for domestic purposes results in a drop in the North-west India groundwater table. 

How to cite: Ajay, A. and Sanyal, P.: An increase in domestic tap water consumption led to a decline in the groundwater reserves of Delhi, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-583, https://doi.org/10.5194/egusphere-egu23-583, 2023.

The arid Tarim River Basin, situated in the Eurasia hinterland, serves as the heart of China’s Silk Road Economic Belt. It covers an area of 1.02 million km² and is surrounded by the Tienshan Mountains to the north, the Kunlun Mountains to the south and the Pamir to the west. During the past few decades, the contradiction between economic growth and environmental protection is particularly evident. For example, the desert riparian forest vegetation has declined along the lower reaches of the Tarim River.

Under global warming, the climate has experienced significant warming and moistening trend during 1961–2018, and the most dramatic increase has occurred since the mid-1980s. The increased precipitation and temperature and the resulted hydrological and ecological changes lead to a hot debate about the “warm–wet” trend. This study systematically investigated the climate change and their impact on hydrological and ecological processes. The temperature increased at a rate of 0.224 ℃ per decade and an evident jump was detected in 1998. For precipitation, about 72.3% meteorological stations experienced significant increase, with an average increasing rate of 7.47 mm per decade. The changes in climatic factors contribute to the changes in the accumulation and ablation of snow and glaciers, which resulted in changes in hydrological processes. The total lake area in the Tarim River has expanded at a rate of 23.79 km² per year during 2012–2021. More specially, the lake area of Ayakum Lake (located near the northern boundary of the Tibetan Plateau) has increased by 50% since 1990, with an increment of 111.61 km² during 1990–2000 and 401.4 km² during2000–2020. The runoffs of the headwaters (i.e., Kaidu River, Aksu River, Yarkant River and Hotan River) of the Tarim River have also increased by a rate of 2.06×10⁸m³, 2.11×10⁸m³, 1.12×10⁸m³ and 2.56×10⁸m³ per decade, respectively.

However, the changes in ecological systems don’t reflect the wetter trend in the Tarim Basin. The negative effects of climate change on the region’s vulnerable ecology have intensified. The snowfall fraction experienced an overall declining trend, increasing at a rate of 0.6% per decade prior to the mid-1990s, followed by a downward trend at a rate of 0.5% per decade. Potential evaporation decreased at a rate of 41.66mm/10a per decade prior to the mid-1990s, and inversed to increase at a rate of 56.68 mm per decade. Prior to 1998, the normalized difference vegetation index (NDVI) of natural vegetation exhibited an increasing trend at a rate of 0.012 per decade, but from 1999 onwards, the NDVI started decreasing at a rate of 0.005 per decade. The bare soil areas of the Taklamakan Desert boundaries expanded by 7.8 % since 1990. Excessive water use, including unrestrained overpumping of groundwater, causes the loss of groundwater.

This study sheds light on the debate of changes in climate and ecological security under global warming in the endoreic Tarim River Basin. However, more efforts should be made on the continuity of these changes, which is crucial for local development and water and ecological security along the Silk Road.

How to cite: Li, W., Li, Z., Chen, Y., and Fang, G.: Is there a turning-point towards improved water and ecological security at the arid Tarim River Basin?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3315, https://doi.org/10.5194/egusphere-egu23-3315, 2023.

Atmospheric water, or non-rainfall water inputs (NRWIs) are a critical, albeit largely overlooked, component of the global hydrological cycle. Water vapor adsorption specifically, is not only the least studied form of NRWI but likely the most common one in arid areas.

Lysimeter measurements in the Negev desert during the summers of 2019-2022 indicate that water vapor adsorption in loess soil amounts to at least 33 mm when looked at cumulatively over the summer (0.3-0.5 mm night^-1): about ~30% of annual rainfall (116 mm). Given the challenges using lysimeter measurements, attempts to quantify NRWI amounts and duration have generally been limited to short time periods at point or local scales. Determining the true importance of NRWIs in arid and extremely arid environments, which comprise 20% of the terrestrial surface, requires new approaches to measure water content in the 0.5-5% range.

Using weighing lysimeters as a reference, we tested of-the-shelf temperature and relative humidity sensors to assess changes in water content with high temporal resolution over longer periods of time for sand and loess soils. Relative humidity was converted to water potential (Kelvin equation). The water content was then determined using a water retention curve measured with a vapor sorption analyzer. Results showed diurnal patterns in water content consistent with lysimeter measurements. Maximum increase in water content correlated well with lysimeter measured NRWIs. While not all issues are yet resolved, this direction opens possibilities to expand our measurement capacity over longer periods of time and increase the number of measurement locations at relatively low cost. This provides one step forward in trying to understand the magnitude of NRWIs in arid environments across the globe.

How to cite: Kool, D. and Agam, N.: Atmospheric water capture by desert soils: can we measure it?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6074, https://doi.org/10.5194/egusphere-egu23-6074, 2023.

The Atacama desert is one of the most promising places on Earth for developing solar power energy due to its aridity, irradiation, and market conditions. However, the high levels of dust attenuate solar power production. This problem is solved by frequent cleaning of the solar panels, which requires a significant amount of water in one of the driest places in the world. Despite the drought condition, the fog and dew formed at the coastal zone of the desert arise as a complementary water source that can potentially be tapped. In this study, we assess the potential of atmospheric water for usage in four solar power plants. We conduct this assessment by combining a satellite-spatial analysis of fog and low cloud frequency, a thermodynamic vertical characterization of the marine boundary layer, and an observational analysis of fog and dew collection using different instruments. Our results reveal that fog and dew are a regular phenomenon in the solar power plants analyzed, being present between 3% and 20% of the year. Oceanic conditions control such phenomena through the inland advection of the marine boundary layer. This layer interacts with a complex topography characterized by natural corridors that allow fog and low clouds to penetrate farther inland. Our observations show that fog and dew are collected mainly during the night, with average rates between 0.1 and 0.2 L m^-2 day^-1. Our research confirms that atmospheric water potential vastly exceeds the solar power plant water demand, demonstrating that atmospheric water is a reliable source for the industry.

How to cite: Lobos Roco, F., Suarez, F., Escobar, R., Osses, P., Ramirez, C., Keim, K., Aguirre, I., Aguirre, F., Vargas, C., Abarca, F., and del Rio, C.: The usage of fog and dew in solar power plants of the Atacama Desert, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9376, https://doi.org/10.5194/egusphere-egu23-9376, 2023.