Prediction of climate change effects on the runoff regime of a forested catchment in northern Iran

Abstract

Abstract:The southern coast of the Caspian Sea in northern Iran is bordered by a mountain range with forested catchments which are susceptible to droughts and floods. This paper examines possible changes to runoff patterns from one of these catchments in response to climate change scenarios. The HEC-HMS rainfall-runoff model was used with downscaled future rainfall and temperature data from 13 Global Circulation Models, and meteorological and hydrometric data from the Casilian (or 'Kassilian') Catchment. Annual and seasonal predictions of runoff change for three future emissions scenarios were obtained, which suggest significantly higher spring rainfall with increased risk of flooding and significantly lower summer rainfall leading to a higher probability of droughts. "Flash floods" arising from extreme rainfall may become more frequent, occurring at any time of year. These findings indicate a need for strategic planning of water resource management and mitigation measures for increasing flood hazards. Prediction of climate change effects on the runoff regime of a forested catchment in northern Iran AbstractThe southern coast of the Caspian Sea in northern Iran is bordered by a mountain range with forested catchments which are susceptible to droughts and floods. This paper examines possible changes to runoff patterns from one of these catchments in response to climate change scenarios. The HEC-HMS rainfall-runoff model was used with downscaled future rainfall and temperature data from 13 Global Circulation Models, and meteorological and hydrometric data from the Casilian (or 'Kassilian') Catchment. Annual and seasonal predictions of runoff change for three future emissions scenarios were obtained, which suggest significantly higher spring rainfall with increased risk of flooding and significantly lower summer rainfall leading to a higher probability of droughts. "Flash floods" arising from extreme rainfall may become more frequent, occurring at any time of year. These findings indicate a need for strategic planning of water resource management and mitigation measures for increasing flood hazards.

Assessment of the flood hazard arising from land use change in a forested catchment in northern Iran

“…The potential for significantly higher peak discharges during the flash floods that climate change predictions suggest will become more common in Casilian Catchment if deforestation occurs (Hajian et al, ) is clear. However, deforestation is a diminishing threat overall due to implementation of more sustainable timber extraction methods, particularly minimum disturbance selective logging (i.e., without creating even local skid trails), and a forthcoming ban on all logging activities.…”

“…These are shown in Table . Secondly, these rainfall depths at each station were interpolated throughout the catchment to produce isohyetal rainfall maps for the different return periods (Hajian, ).…”

“…The southern edge of the catchment is defined by the Mirozad and Golrad mountains (2,700 and 3,349 m, respectively; Figure 2b) but the elevations of the mountain peaks progressively reduce northwards (downstream) towards the Caspian Sea. Further characteristics of the catchment were reported by Hajian et al (2016).…”

“…Tamab, Iran's Water Resources Research Organisation based in Tehran, provided most of the data for this study. The mean annual rainfall for the catchment was around 756 mm (1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996) inclusive) with a mean annual runoff of around 230 mm and a mean discharge from the catchment that varies seasonally between around 0.3 and 0.6 m 3 /s (Hajian et al, 2016; Table 1).…”

“…HEC‐HMS contains a much wider range of modelling options than SWAT and many similar models, including an option to use the CN method for determining the direct storm runoff from a catchment. Its data requirements are much greater than SWAT, requiring careful optimisation and calibration with the possible risk of structural non‐identifiability (Shin et al, ), but it has been successfully used in a wide range of global contexts (e.g.,northwestern USA—McColl & Aggett, ; eastern China—Chen, Xu, & Yin, ; Kenya—Olang & Fürst, ; eastern India—Sanyal, Densmore, & Carbonneau, ; Greece—Papathanasiou, Makropoulos, & Mimikou, ; El Salvador—Tellman et al, ; northern Iran—Hajian et al, ).…”