Impacts of Multi-year Droughts and Upstream Human-Induced Activities on the Development of a Semi-arid Transboundary Basin

This paper aims at investigating the combined impacts of basin-wide multi-year droughts and upstream human-induced activities on current and future potential development of a semi-arid transboundary basin. The approach is based on the drought analysis through three widely used drought indices (Standardised Drought Index- SPI, Reconnaissance Drought Index - RDI and Streamflow Drought Index- SDI), coupled with the current and future conceivable man-made changes upstream, taking also into account the effects of climate change. As a representative case, the Diyala river basin, shared between Iraq and Iran, is selected. A close examination of the climate trends in the study area exhibits that the basin points to be drier, with a decreasein precipitation and rise in the rates of temperature and potential evapotranspiration. The comparison between RDI and SDI indicates the cumulative drought effects on runoff during recent multi-year droughts episodes (1999–2001 and 2008–2009), which crippled the socio-economic activities and influenced the environmental system. Further, the results reveal that the combined impacts of multi-year droughts at basin scale and the river damming, water abstraction and water diversion works upstream have significant effects on water availability, especially at the middle and lower parts of the basin, with impacts on the security of the irrigated agriculture and public water supply, contributing to displacement and tribal conflicts. The projected climate change conditions along with the water withdrawal schemes upstream, which will put into operation in the foreseeable future, are expected to increase the vulnerability of water security in the portion of the basin that lies in the downstream country.