Abstract
Modeling the hydrologic responses to future changes of climate is important for improving adaptive water management. In the present application to the Zarrine River Basin (ZRB), with the major reach being the main inflow source of Lake Urmia (LU), firstly future daily temperatures and precipitation are predicted using two statistical downscaling methods: the classical statistical downscaling model (SDSM), augmented by a trend-preserving bias correction, and a two-step updated quantile mapping (QM) method. The general circulation models (GCM) input to SDSM are climate predictors of the Canadian Earth System Model (CanESM2) GCM under the representative concentration pathway (RCP) emission scenarios, RCP45 and RCP85, whereas that to the QM is provided by the most suitable of several Climate Model Intercomparison Project Phase 5 (CMIP5) GCMs under RCP60, in addition. The performances of the two downscaling methods are compared to each other for a past “future” period (2006–2016) and the QM is found to be better and so is selected in the subsequent ZR streamflow simulations by means of the Soil and Water Assessment Tool (SWAT) hydrological model, calibrated and validated for the reference period (1991–2012). The impacts of climate change on the hydrologic response of the river basin, specifically the inflow to the Boukan Reservoir, the reservoir-dependable water release (DWR), are then compared for the three RCPs in the near- (2020–2038), middle- (2050–2068) and far- (2080–2098) future periods assuming (1) the “current” consumptive demand to be continued in the future, and (2) a more conservative “recommended” demand. A systematic future shortage of the available water is obtained for case (1) which can be mitigated somewhat for (2). Finally, the SWAT-predicted ZRB outflow is compared with the Montana-based estimated environmental flow of the ZR. The latter can successfully be sustained at good and fair levels for the near- and middle-future periods, but not so for the summer months of the far-future period, particularly, for RCP85.
Highlights
Climate predictions of general circulation models (GCMs) indicate a profound variability of future precipitation and temperatures in terms of trends and extremes which, eventually, will increase the likelihood of severe and irreversible impacts on the ecosystem, including rivers and lakes [1].Historical observations over the last century have confirmed the impacts of a changing climate, as the average surface temperature increased globally by about 0.74 ◦ C between 1905 and 2005 and, the globally averaged warming rate has almost doubled over the last 50 years, 1965 to2005 [2]
The pressures of climate change on hydrology and water availability, in particular, are especially high in countries across the Middle East and North Africa (MENA) region, including Iran, as the most water-scarce regions in the world, not least due to high population growth [6] which leads to increasing water demand, while often facing, at the same time, poor water resources management
The statistical downscaling model (SDSM)-downscaling model is calibrated on observed data for the 13-year period 1987–1999 and validated for the 5-year period 2000–2005
Summary
Climate predictions of general circulation models (GCMs) indicate a profound variability of future precipitation and temperatures in terms of trends and extremes which, eventually, will increase the likelihood of severe and irreversible impacts on the ecosystem, including rivers and lakes [1].Historical observations over the last century have confirmed the impacts of a changing climate, as the average surface temperature increased globally by about 0.74 ◦ C between 1905 and 2005 and, the globally averaged warming rate has almost doubled over the last 50 years, 1965 to2005 [2]. The pressures of climate change on hydrology and water availability, in particular, are especially high in countries across the Middle East and North Africa (MENA) region, including Iran, as the most water-scarce regions in the world, not least due to high population growth [6] which leads to increasing water demand, while often facing, at the same time, poor water resources management. Because of this situation, countries like Iran are highly vulnerable to the impacts of climate change [7], including a higher frequency of natural disasters and food insecurity
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