| Dam-triggered human interactions in the form of an artificial lake creation, expansion of irrigation and downstream urbanization are precipitation-changing land use land cover (LULC) change drivers for impounded basins. A set of hypothesis involving the various anticipated changes around dams were put forward to help capture the sensitivity of each one of these changes to extreme precipitation (EP) modification. Subsequently, various scenarios of LULC change were analyzed in a step by step fashion to elucidate the scenario leading to most significant impact on EP. The particular LULC scenarios included 1) the control scenario representing the contemporary land-use, 2) the pre-dam scenario representing the natural landscape before the construction of the dams, 3) the non-irrigation scenario representing the condition where previously irrigated landscape in the control is transformed to the nearby land-use type, and 4) the reservoir-double scenario with the size of the reservoir doubled from the original.;A coupled numerical modeling and observational approach was adopted to analyze the impact of these LULC scenarios in two modes. In the first mode (called normal), the probable precipitation pattern due to each LULC scenario was identified. In the second mode (called moisture-maximized), the extreme pattern represented from a 100% relative humidity profile, was generated as an indicator of EP. The results demonstrated that LULC changes driven by dams can in fact alter the local to regional hydrometeorology as well as EP. In general, there was an observed increase within a range of 2% to 10% in EP in the post-dam era as compared to the pre-dam. This range is significant as it represents the far right tail of the frequency/probability distribution. Dams in certain climatic zones and terrain features were particularly found sensitive to modification of EP motivated by LULC changes. A region with semi-arid climate on a leeward side and flat terrain was found to impact EP much greater than the one characterized by temperate climate on windward side of a mountainous terrain. All in all, there is a strong possibility of a positive feedback mechanism initiated by dam-driven LULC changes; with irrigation intensifications being the most dominant followed by the pre-dam conditions, and finally the reservoir size variations. Inter--decadal observational and modeling analysis also indicated that LULC changes can modulate the synoptic and inland patterns of synoptic systems such as Atmospheric Rivers (ARs). |
