Abstract
Abstract This study evaluates the impacts of climate change on water supply and demand of the Nebhana dam system. Future climate change scenarios were obtained from five general circulation models (GCMs) of CMIP5 under RCP 4.5 and 8.5 emission scenarios for the time periods, 2021–2040, 2041–2060 and 2061–2080. Statistical downscaling was applied using LARS-WG. The GR2M hydrological model was calibrated, validated and used as input to the WEAP model to assess future water availability. Expected crop growth cycle lengths were estimated using a growing degree days model. By means of the WEAP-MABIA method, projected crop and irrigation water requirements were estimated. Results show an average increase in annual ETo of 6.1% and a decrease in annual rainfall of 11.4%, leading to a 24% decrease in inflow. Also, crops' growing cycles will decrease from 5.4% for wheat to 31% for citrus trees. The same tendency is observed for ETc. Concerning irrigation requirement, variations are more moderated depending on RCPs and time periods, and is explained by rainfall and crop cycle duration variations. As for demand and supply, results currently show that supply does not meet the system demand. Climate change could worsen the situation unless better planning of water surface use is done.
Highlights
A combination of climate change and increase in irrigation usage is likely to substantially decrease fresh water availability, especially in Mediterranean regions, which would lead to the largest decreases in the world (Cramer et al )
The findings of this study agree with the results reported by Pathak & Stoddard ( ), who pointed out that the tomato growing season length in California would be reduced between 11 and 13% under RCP 4.5 and between 13 and 14% under RCP 8.5
This study examined the impacts of climate change on the irrigation supply and demand of the Nebhana dam system
Summary
A combination of climate change and increase in irrigation usage is likely to substantially decrease fresh water availability (by 2–15% for 2 C of warming), especially in Mediterranean regions, which would lead to the largest decreases in the world (Cramer et al ) These regions are likely to warm at a rate about 20% greater than the global annual mean surface temperature (Lionello & Scarascia ). Policies need to mitigate these risks and consider adaptation options; decisionmakers currently lack adequate information, in the south Mediterranean regions where impact assessment studies are limited (Cramer et al ) In these regions, the use of water management tools, taking into consideration water supply and demand variability in an integrated way, are needed. Water Evaluation and Planning software (WEAP) is a modelling decision support system that helps assess climate, hydrology, land use, infrastructure and management priorities at regional levels
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