Hydro-climatic changes in irrigated world regions

Abstract: Understanding of hydro-climatic changes in the world’s river basins is required to ensure future food security. Different regional basins experience different levels of hydro-climatic change depending on the endorheic or exorheic nature of a hydrological basin, along with the climatic conditions and human land and water-use practices, for instance for irrigation. This thesis has analyzed long-term hydro-climatic changes in two main irrigated regions of the world: the Mahanadi River Basin in India and the Aral region in Central Asia. Thesis applies a basin-wise, data-driven water balance-constrained approach to quantifying the hydro-climatic changes, and to distinguish their main drivers in the past century and for future. Results point at human water-use and re-distribution for irrigation within a basin as a major driver of water balance changes, which also affect surface temperature in the region.Cross-regional comparison focused on the climatically important changes of water, vapor and latent heat fluxes at the land surface, and also on the changes to water resource availability in the landscape. Results show that irrigation- driven changes in evapotranspiration, latent heat fluxes and associated temperature changes at land surface may be greater in regions with small relative irrigation impacts on water availability in the landscape than in regions with severe such impacts. This implies that one cannot from the knowledge about only one aspect of hydro-climatic change simply extrapolate the impact importance of those changes for other types of water changes in a region.Climate model projections results show lack of consistency in individual GCM performance with regard to temperature and to precipitation, implying difficulties to identify well-performing GCMs with regard to both of these variables in a region. In Aral region, the thesis shows that ensemble mean of different GCM outputs may provide robust projection of future hydro-climate changes.