Implementation of a new crop phenology and irrigation scheme in the ISBA land surface model using SURFEX_v8.1

Abstract

Abstract. With an increase in the number of natural processes represented, global land surface models (LSMs) have become more and more accurate in representing natural terrestrial ecosystems. However, they are still limited with respect to the impact of agriculture on land surface variables. This is particularly true for agro-hydrological processes related to a strong human control on freshwater. While many LSMs consider natural processes only, the development of human-related processes, e.g. crop phenology and irrigation in LSMs, is key. In this study, we present the implementation of a new crop phenology and irrigation scheme in the ISBA (interactions between soil–biosphere–atmosphere) LSM. This highly flexible scheme is designed to account for various configurations and can be applied at different spatial scales. For each vegetation type within a model grid cell, three irrigation systems can be used at the same time. A limited number of parameters are used to control (1) the amount of water used for irrigation, (2) irrigation triggering (based on the soil moisture stress), and (3) crop seasonality (emergence and harvesting). A case study is presented over Nebraska (USA). This region is chosen for its high irrigation density and because independent observations of irrigation practices can be used to verify the simulated irrigation amounts. The ISBA simulations with and without the new crop phenology and irrigation scheme are compared to different satellite-based observations. The comparison shows that the irrigation scheme improves the simulated vegetation variables such as leaf area index, gross primary productivity, and land surface temperature. In addition to a better representation of land surface processes, the results point to potential applications of this new version of the ISBA model for water resource monitoring and climate change impact studies.

Implementation and sensitivity analysis of the Dam-Reservoir OPeration model (DROP v1.0) over Spain

“…Furthermore, the results highlight the importance of incorporating reservoir operations into large-scale hydrological models for a more realistic representation of river flows and thus the water mass exchange with oceans and the atmosphere. The physical approach of DROP is consistent with that of the ISBA-CTRIP LSM RRM (land surface-river routing model): irrigation demands used as input to the reservoir model can be simulated by the irrigation module recently integrated into ISBA (Druel et al, 2022), and CTRIP already includes a lake model, "MLake" (Guinaldo et al, 2021), that a priori models inland water bodies at a global scale, calculates mass balance and lake outflow at the global scale, and provides the foundation for integrating human reservoir operations. The next step is to implement the DROP model in MLake and create a link between the two anthropization models by coupling the new versions of ISBA (irrigation) and CTRIP (reservoirs).…”

“…Since dams provide water for the downstream demand within a certain distance, a maximum distance, d max , is a parameter to define, for each reservoir, the irrigated grid cells within the river basin to be supplied and thus delimits a "command area" for each reservoir. In contrast to Hanasaki et al (2006) (where a crop growth model is considered to calculate the irrigation demand), here the distribution of irrigated areas is based on ECOCLIMAP SG (Calvet and Champeaux, 2020;Druel et al, 2022), which is used by the irrigation module in the ISBA LSM (Druel et al, 2022) to compute irrigation demands for 5 × 5 km-resolution grid cells (see Sect. 3).…”

“…-Simulated irrigation demands. The irrigation water demands are simulated by the new irrigation scheme implemented in the ISBA LSM (Druel et al, 2022). It uses the ECOCLIMAP-SG land cover classification to identify the areas within the grid cell that can be irrigated.…”

“…However, some simplifications are to be noted which could be improved in the future. The irrigation water demand estimation is based on the irrigation scheme in ISBA LSM, which has its own limitations (Druel et al, 2022). Also, in this version of the reservoir scheme, water demands for each irrigation reservoir are reduced to considering pixels that are downstream of the reservoir at a given maximum distance d max .…”

“…However, once the DROP model is implemented in a hydrological model, the tributary inflows will correspond to river flows simulated by the routing model, and therefore there should be a deterioration of the performance index on discharge with an error spreading along the anthropized rivers. However, by coupling the above with a model that takes irrigation into account, such as the new version of the ISBA land surface model, for example (Druel et al, 2022), the water releases from the reservoir model can be linked to crop irrigation needs, and thus river water withdrawals can be represented as well as those taken directly from the reservoirs.…”