HS2.1.4

This study aims to analyze the main components of the energy and hydric budgets of irrigated maize in southwestern France. To this objective, the ISBA-A-gs (Interactions between Soil, Biosphere, and Atmosphere) is run over six maize growing seasons. As a preliminary step, the ability of the ISBA-A-gs model to predict the different terms of the energy and water budgets is assessed thanks to a large database of in situ measurements by comparing the single budget version of the model with the new Multiple Energy Balance version solving an energy budget separately for the soil and the vegetation. The in situ data set acquired at the Lamasquere site (43.48^o N, 1.249^o E) includes half-hourly measurements of sensible (H) and latent heat fluxes (LE) estimated by an Eddy Covariance system. Measurements also include net radiation (Rn), ground heat flux (G), plant transpiration with sap flow sensors, meteorological variables, and 15-days measurements of vegetation characteristics. The seasonal dynamics of the turbulent fluxes were properly reproduced by both configurations of the model with an R² ranging from 0.66 to 0.89, and a root mean square error lower than 48 W m^-2. Statistical metrics showed that H was better predicted by MEB with R² of 0.80 in comparison to ISBA-Ags (0.73). However, the difference between the RMSE of ISBA-Ags and MEB during the well-developed stage of the plants for both H and LE does not exceed 8 W m^-2. This implies that MEB only has a significant added value over ISBA-Ags when the soil and the canopy are not fully coupled, and over a heterogeneous field. Furthermore, this study made a comparison between the sap flow measurements and the transpiration simulated by ISBA-A-gs and MEB. A good dynamics was reproduced by ISBA-A-gs and MEB, although, MEB (R²= 0.91) provided a slightly more realistic estimation of the vegetation transpiration. Consequently, this study investigated the dynamics of the water budget during the growing maize seasons. Results indicated that drainage is almost null on the site, while the observed values of cumulative evapotranspiration that was higher than the water inputs are related to a shallow ground table that provides supplement water to the crop. This work provides insight into the modeling of water and energy exchanges over maize crops and opens perspectives for better water management of the crop in the future.

How to cite: Dare-Idowu, O., Jarlan, L., Brut, A., Le-Dantec, V., Rivalland, V., Ceshia, E., and Boone, A.: Hydrological functioning of irrigated maize crops in southwest France using Eddy Covariance measurements and a land surface model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15262, https://doi.org/10.5194/egusphere-egu21-15262, 2021.

In recent decades, saline lakes are being globally shrunk at alarming rates due to the combined effect of global warming and long-term water mismanagement to support agriculture and industrial demand. These factors have altered the fragile balance of these ecosystems triggering serious environmental issues. A well-known case in the Southwestern US is the Salton Sea, the largest lake in California. While the Salton Sea Basin (SSB) is considered as one of the most productive agricultural regions in North America, improvements in the agricultural water use efficiency to sustain and increase food production have imbalanced the lake’s water budget. Lake's water level has declined by 33% between 2000 and 2018 causing increases in salinity and anoxia, and the spreading of toxic dust from the exposed playa. Considering the key role of the Salton Sea in ecohydrological regulation and the wide spectrum of ecosystem services (e.g., wildlife habitat, transport, recreation), greater science-based efforts are needed to formulate timely adaptation and mitigation strategies for lake restoration and conservation. However, prior to formulating these strategies, it is crucial to understand the hydrologic response mechanisms of the basin to natural and anthropogenic stressors as well as the historic causal factors that have dictated its environmental deterioration. In this study, we developed a semi-distributed modeling framework using the Soil and Water Assessment Tool (SWAT) to quantify the regional water balance and understand interrelationships among ecological, hydrological, and human-impact variables. Preliminary results determined that the water contribution from the major lake tributaries has not been significantly affected over time and the imbalances in the lake’s water budget may be associated with changes in groundwater-surface water interactions due to agricultural water management. The final results of this study are expected to assist decision-makers with a robust modeling tool to evaluate the environmental tradeoffs in implementing distinct management alternatives across SSB while minimizing its economic consequences.

How to cite: Acero Triana, J. S. and Ajami, H.: Understanding the Hydrologic Response Mechanisms of California’s Largest Lake in a Highly Managed Endorheic Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-371, https://doi.org/10.5194/egusphere-egu21-371, 2021.

Mulberry-based fish ponds are representative traditional eco-agriculture in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA). Investigations about the changes in such ponds and their relevant water environment under the background of rapid urbanization can provide a reference for the protection and development of these ponds. Using the Landsat images obtained after 1986, this study employed supervised classification and visual interpretation approaches and water intensity index as well as calculating synthesized index to identify the spatial patterns of changes in Mulberry-based fish ponds in the GBA. The results indicated that the year of 2013 was the inflection point of fish pond changes, which can also be proved by calculating synthesized index. The causes to the changes in fish ponds were further explored from four aspects: land use change, industrial transfer, government guidance and financial motives.

How to cite: Zhang, W., Cheng, Z., Liu, X., Lin, G., He, J., Huang, F., and Yang, X.: The changes in Mulberry-based fish ponds in the Guangdong-Hong Kong-Macao Greater Bay Area over the past 40 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-330, https://doi.org/10.5194/egusphere-egu21-330, 2021.

On the floodplains of the Cambodian Mekong Delta, rainfed and irrigated dry-season agriculture is a crucial source of revenue for the local population. Traditional rice production is being progressively complemented by the cultivation of higher-value crops like maize, fruit trees and vegetables. Fundamentally, the annual monsoon regime and the resulting flood dynamics determine the framework for these agricultural practices, with a wet season lasting from June to November and a peak high flow reached in September. Rice is cultivated after flood recession in lower-lying areas. On higher terrain, fruit trees and vegetables are widely irrigated by farmers using individual pumps to lift water from large-scale communal channels.

However, in recent years, various drivers of change have impacted these long-established dynamics. Climate change is causing shifting precipitation patterns and a modification of annual flow regimes in the Mekong river and its deltaic distributaries. In addition, the irrigation channel infrastructure is being largely rehabilitated by both local initiatives and international development agencies. These measures are rapidly changing the conveyance network for inundation, drainage, and irrigation on the floodplains, with proportions and consequences which are yet unknown. Finally, land use changes driven by market forces - such as the shift to cash crops like mango trees - are modifying the crop water demand in the area. 

In this context, the present study aims to provide a thorough understanding and quantification of the effects of these changes with regard to crop water requirements, irrigation efficiency, and agricultural productivity. Extensive fieldwork was carried out on a 44-km² area to gather knowledge of agricultural practices (especially irrigation) and to identify the main local hydrological objects and drivers. The land use and seasonal inundation extents were characterized through remote sensing analyses, using optical Sentinel-2 and synthetic aperture radar (SAR) Sentinel-1 images. On that basis, an eco-hydrological model is being developed on the generic software platform OpenFLUID, explicitly representing the hydraulic connections and irrigation decisions. This tool will be used to highlight possible salient control factors for hydrological processes, and to simulate the direct and indirect effects of climate change scenarios, irrigation and water power infrastructure development, and land use changes on local hydrology, irrigation, and agricultural productivity. 

How to cite: Orieschnig, C. A., Belaud, G., Venot, J.-P., and Massuel, S.: Cultivated floodplains of the Cambodian Mekong delta: understanding the changing balance between the flow regime and the agricultural practices, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1248, https://doi.org/10.5194/egusphere-egu21-1248, 2021.

Nutrient loss from agricultural fields imparts increased fertilizer costs as well as negative consequences for the natural environment. Given that water availability mediates both nutrient uptake by plants as well as nutrient leaching, we hypothesize that hydrologic conditions can explain variations in nutrient use efficiencies, defined as ratios of the nutrient amounts in harvested yield and in inputs. We analyze data from 110 US catchments with agricultural area comprising more than 10% of the watershed and compute nitrogen and phosphorus use efficiencies (NUE and PUE) over the period 1988-2007. To assess if NUE and PUE are related to hydrologic conditions, we consider the evaporative ratio ET/P (calculated as evapotranspiration divided by precipitation) as a predictor in a linear mixed effect model. We test the hypotheses that the nutrient use efficiencies increase with ET/P, through increased water and nutrient retention, and that the nutrient efficiencies increase through time. We found that both nutrient use efficiencies increased through time: NUE increased in the period analyzed in 88% of catchments, while PUE in 90% of catchments. Both NUE and PUE were largely driven by significant increases in N and P amounts in yield. The evaporative ratio was positively related to NUE. Moreover, we found an interaction between ET/P and time, such that the ET/P effect on NUE decreased in the period 1998–2007. The evaporative ratio was also positively related to PUE. Other potential drivers were assessed, including interaction between ET/P and time, as well as the percentage of agricultural area in each catchment. Our results show that changes in climate that include increased evaporation and decreased precipitation can lead to increase N use efficiencies without decreasing yields. The implications of our findings in terms of the release of N and P to water bodies has particular relevance in terms of climate change, as higher temperatures and lower precipitation (i.e. increasing evaporative ratios) will potentially lead to increased nutrient retention and therefore decreased nutrient leaching from agricultural fields.

How to cite: Scaini, A. and Manzoni, S.: Are catchment-scale nitrogen and phosphorous use efficiencies controlled by climate?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4453, https://doi.org/10.5194/egusphere-egu21-4453, 2021.

The Czech Republic is an intensely agricultural country. Agricultural intensification of the Czech Republic started in the 1970s during the Communist regime wherein large monotonous agricultural fields, subsurface tile drainage systems, and artificially straightened streams were incorporated across the landscape. Since 1989 (the end of the Communist era), agricultural land and management has been privatized and has experienced shifts from centrally planned crop rotations to those that are economically-driven. On the other hand, nowadays many Czech farmers are beginning to explore various agricultural conservation practices which can have as significant of an impact as land use changes. The purpose of this study is to determine the effects of various agricultural conservation practices (contour tillage, reduced tillage, and grass strip addition) and decreasing field sizes at the farm scale in a representative agricultural basin in the Czech Republic. We conducted scenario analysis using the Soil and Water Assessment Tool (SWAT) to determine the effects of these measures on basin water balance and soil erosion. Through SWAT we were able to determine which measures are most effective when combined at the farm-scale.

Acknowledgment: The presented research has been performed within project H2020 No. 773903 Shui, focused on water scarcity in European and Chinese cropping systems and the Grant Agency of Czech Technical University in Prague, No. SGS20/156/OHK1/3T/11.

How to cite: Noreika, N., Li, T., Zumr, D., krása, J., and Dostál, T.: The Effects of Agricultural Conservation Practices on the Local Water Cycle in conditions of the Czech Republic Modeled by SWAT, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4972, https://doi.org/10.5194/egusphere-egu21-4972, 2021.

Changing weather patterns and anthropogenic land use change significantly alter the terrestrial water cycle. A key variable that modulates the water cycle on the land surface is soil moisture and its variability in time and space. Hydrological models are used to simulate key components of the water cycle including infiltration, soil storage and uptake by plants. However, uncertainties remain in accurately representing soil moisture dynamics in models. Here, with the aid of several sensors installed at a 30-ha experimental research facility, we attempt to quantify differences in soil water storage across multiple land use types – cropped area, mosaic of turf grass and native plants, and an unkept weeded area as control land use. We will also discuss the accuracy of sensors to correctly measure soil water storage. Our study was conducted at an agricultural experimental station in Columbia, Missouri, USA. We use a variety of instruments to measure weather, evapotranspiration, and soil water. We used boundary layer scintillometers to measure near-surface turbulence, sensors to continuously track soil moisture and temperature, as well as weather stations for precipitation, air temperature, solar radiation and wind speed.  Changes in volumetric water content and soil temperature are measured at 5-minute intervals at 10-, 20-, and 40-cm soil depths to compare soil water storage among the three land use types. We also took soil samples before and after several storm events to calibrate the sensor readings at three sites. We, then, analyzed several storm events over a period of five months and compared the actual soil moisture and soil temperature dynamics at finer time intervals. With additional measurements of weather and boundary layer turbulence, we hope to reveal the landscape and weather control on soil moisture distribution across multiple land uses, and their subsequent impact on plant water uptake. Our preliminary results indicate that continuously disturbed agricultural lands depletes soil moisture at faster rates, which may present challenges in maintaining land productivity in the long term.

How to cite: Fritz, V., Thaasan, T., Williams, A., Udawatta, R., Mendis, S., and Aloysius, N.: Elucidating soil moisture dynamics in agricultural landscapes under varying weather patterns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5876, https://doi.org/10.5194/egusphere-egu21-5876, 2021.

Monitoring soil water status is one key option to optimise water use in agriculture. Soil moisture sensors are widely used for investigating available soil water to optimally adapt irrigation scheduling to crop water requirements. Although reliable measurements are subject to proper soil-specific calibration of sensors, meaningful calibration functions are not always available. Another question is the plausibility of soil water monitoring under field conditions. The objective of this study was to calibrate four multi-sensor capacitance probes in the laboratory and  to evaluate the calibrated water content readings under natural conditions in an irrigated field by means of a modelling approach.

The multi-sensor capacitance probes (SM1 by ADCON Telemetry) were of 90 cm length and contained nine sensors (S1 to S9) at 10 cm spacing. The digital output values were given in scaled frequency units (SFU). The laboratory calibration was carried out on sandy loam and sand. Measurements were undertaken by placing the probes inside a PVC tube backfilled with soil at different water contents. Soil samples were collected using metallic cylinders of 250 cm³, from which volumetric water content (θ) was determined gravimetrically. The sensor readings in soil were normalised by using sensor readings in air and water as lower and upper limit, respectively. The pairs of measured θ and normalised SFU were related to each other by curve fitting. For each soil type, eight sensor-specific calibration functions were developed that allowed the calculation of θ in cm³ cm⁻³ from SM1 readings.

After calibration, the SM1 probes were installed in a field in Obersiebenbrunn, Lower Austria, where sandy loam is the main soil. Three of the probes monitored irrigated plots and the fourth a rainfed plot. To obtain reference values, one HydraProbe soil moisture sensor (Stevens Water Monitoring Systems) was installed in 20 cm depth, near each SM1. The average daily θ-values from the S2 (20 cm depth) contained in each SM1 probe were compared to the water fraction collected with the corresponding HydraProbe. Moreover, the SM1 θ-values were used to determine the daily soil water depletion in the root zone (Dr) for a rooting depth of 1 m. The obtained Dr datasets were compared to Dr simulated using CROPWAT 8.0 by FAO.

The field results showed that the SM1 probes were able to reproduce the HydraProbe dynamics of wetting and drying periods during the crop season. Nevertheless, a considerable difference was noted between the sensor measurements. The SM1 overestimated θ in the irrigated plots, whereas it underestimated θ in the rainfed plot. The discrepancies can be attributed mainly to the different physical mechanisms behind the sensors and to the unfeasible reproduction of field bulk density and soil structure in the laboratory. Furthermore, the operational frequency and permittivity response of the SM1 probes should be revised for future versions. The simulation results showed that the observed Dr values were more consistent with CROPWAT Dr results at the end of the simulation period, suggesting that the SM1 required several weeks to consolidate and give representative θ-values for the soil profile.

How to cite: Morales Santos, A. G. and Nolz, R.: Soil water content sensors from laboratory calibration to field monitoring: discrepancies and uncertainties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10089, https://doi.org/10.5194/egusphere-egu21-10089, 2021.

Climate change is projected to result in higher temperatures, higher annual precipitation and more uneven distribution of precipitation in the northern regions. This requires adaptation in agriculture where both excessively wet and dry cycles pose challenges to cropping. Until now, water management in northern agricultural fields has been resting primarily on efficient drainage, but interest towards more flexible measures has increased.

This study focuses on the hydrological effects of climate change and controlled drainage operated with subsurface drains and an open collector ditch in an agricultural field. The objective was to computationally estimate how groundwater levels and water balance respond to controlled drainage and open ditch scenarios in climate conditions projected to take place in Finland during this century. A hydrological model FLUSH was used to simulate the hydrology of an experimental field in Sievi, Northern Ostrobothnia, Finland during years 1970–2100. Down-scaled climate projections from EURO-CORDEX (RCP 8.5 and RCP 2.6) were used as meteorological input. The temporal development of the field hydrology and the effects of controlled drainage were examined by dividing the time series into four subsequent time intervals (historical period and three future periods).

Two different control scenarios were studied. Drainage intensity was reduced during growing seasons in summers (Jun.–Aug.) and either in autumn (Oct.–Nov.) or from autumn to spring (Oct.–Mar.). During these periods, groundwater table was on average 17–29 cm, 28–30 cm and 36–40 cm higher, respectively, in the control scenarios when compared to conventional subsurface drainage in different study intervals and emission scenarios. The implementation of controlled drainage reduced annual drain discharge by 21–46 mm. The projected temporal evolution of the effects of controlled drainage on groundwater levels and annual drain discharges were not monotonous, but the projected effects were larger during the future periods when compared to the historical period. Controlled drainage effect on groundwater levels was seen during both dry and wet years. Controlled drainage was assessed to be an effective method to control field water processes currently and in the future decades. The open collector ditch lowered groundwater levels within a distance of 115 m from the ditch.

How to cite: Salla, A., Salo, H., and Koivusalo, H.: Controlled drainage in future climate scenarios, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14381, https://doi.org/10.5194/egusphere-egu21-14381, 2021.

Food security is an increasing threat to rice-consuming nations in the face of a changing climate. In this study, we present a framework for analysing  the historical and projecting the future relationship between climate variability and rice yield in the context of weather index insurance. The case study is the Muda rice granary, the largest rice paddy planting area in Malaysia producing approximately 40% of the national output. First, correlation and linear regression are used to explore the response of seasonal rice yield to various average and extreme precipitation, temperature and streamflow-based indices over a 16 year period between 2001 to 2016.  The highest Pearson correlation (r) and coefficient of determination (R²) values were obtained with June minimum temperature in the dry season, and December maximum 1 day precipitation and  January mean streamflow in the wet season. The results suggest that rice yield is most at risk from the impact of hydroclimatic variability and change during the flowering and maturity stages of crop growth. Next, findings from the statistical analysis are integrated with hydro-crop simulation of the 4,515 km2 catchment area, using a calibrated Soil Water Assessment Tool (SWAT) and bias-corrected Regional Climate Model output from the Coordinated Regional Downscaling Experiment for South East Asia (CORDEX-SEA). The output is finally used to construct projected future risk profiles for rice production in the area. 

How to cite: Zulkafli, Z., Raffar, N., Abdi, M. J., Jajarmizadeh, A., Ahmad Shukri, M. S., Muharam, F. M., Nurulhuda, K., Rehan, B. M., Chung, J. X., Liew, J., and Tangang, F.: Historical and projected future hydroclimatic risk on seasonal yield in the irrigated rice paddies of Malaysia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15844, https://doi.org/10.5194/egusphere-egu21-15844, 2021.