The Impact of Climate Change as Well as Land-Use and Land-Cover Changes on Water Yield Services in Haraz Basin

Water-yield assessment is crucial to effectively achieve water supply management at the basin scale. It is affected by climate change, and Land Use/Land Cover Change (LULCC). This paper quantifies the combined impact of LULCC and climate change on water yield over short and long-term periods in the Haraz basin, Iran. This basin has experienced severe forest degradation, agricultural expansion, and urbanization. Most agricultural lands are within the plains and coastal areas, and 25% of the basin is covered by forest, which includes part of the Hyrcanian conservation forests. Four scenarios to distinguish the relative portion of Land Use/Land Cover (LULC) and climate for water supply variations are considered, including real conditions at the beginning of the period (Sn1), real conditions without changes in LULC (Sn2), real conditions without climate change (Sn3), and real conditions at the end of the period (Sn4). Four study periods include 1992-2007, 2007-2016, 2016-2026 as a short term, and 1992-2026 as a long-term period. The spatial patterns of annual precipitation showed decreasing amounts in the three studied years from the northwest to the south. Water yield also reduced during the study period 1992-2007 and 2007-2016, and climate change plays an essential role in this reduction. Forecasts show that rainfall will recover in 2026 and water yield will increase in the northern sub-basins. In the long run, from 1992 to 2026, the contribution of LULCC and climate change factors to water yield are equal. The results can provide references for land use management to enhance water yield considering global climate change.