Investigation of effects of land cover and climate change on river flow (Case study: Minab watershed)
Barkhordary Jalal khosroshahi Mohammad
ABSTRACT:
This is illustrated by frequent occurrences of severe droughts and floods. The challenge is to determine whether these hydrological hazards and disasters are the result of climatologic variability or of man-induced changes. This study provides an alternative approach to assess the actual changes in hydrologic response of a watershed in an arid tropical region to land use transformations made in the past 25 years. The approach combines remotely sensed image data from satellites with in-situ hydrological observations from the Minab catchment's (ca. 1.106 ha). Results of long-term analysis of historical time series on rainfall, land use and stream flow are integrated at the landscape level, to identify appropriate options for land and water management. In 1976, about 45 percent of the watershed area was covered by rangeland and natural forest. Due to continued overgrazing, rangeland cover decreased to 8 percent in 2002. Three main land use classes have replaced these fertile rangelands. These are: poor natural cover, agricultural area and residential area. The destruction of natural vegetation resulted in a decrease of the annual total water yield by 3.4 mm, with a decrease in the base flow during the low-flow period (May-November) and an increase in the storm runoff during the high-flow period (December to April). It can be concluded that climatic variability and land use change are the most important factors affecting the (changes in the) hydrologic regime of the Minab catchment's. For a flood return period of more than 10 years, (high) rainfall intensity as a climatic factor is considered dominant. For a return period of less than 10 years in combination with a low flow period, land use change is the dominant factor determining the flow regime. An active management strategy aimed at the conservation and regeneration of the natural vegetation is recommended, in order to improve the distribution of water throughout the entire Minab catchment's, during both dry and wet periods.
Keywords: Land cover change, climatic variability, catchment hydrology, remote sensing, GIS
ABSTRACT:
This is illustrated by frequent occurrences of severe droughts and floods. The challenge is to determine whether these hydrological hazards and disasters are the result of climatologic variability or of man-induced changes. This study provides an alternative approach to assess the actual changes in hydrologic response of a watershed in an arid tropical region to land use transformations made in the past 25 years. The approach combines remotely sensed image data from satellites with in-situ hydrological observations from the Minab catchment's (ca. 1.106 ha). Results of long-term analysis of historical time series on rainfall, land use and stream flow are integrated at the landscape level, to identify appropriate options for land and water management. In 1976, about 45 percent of the watershed area was covered by rangeland and natural forest. Due to continued overgrazing, rangeland cover decreased to 8 percent in 2002. Three main land use classes have replaced these fertile rangelands. These are: poor natural cover, agricultural area and residential area. The destruction of natural vegetation resulted in a decrease of the annual total water yield by 3.4 mm, with a decrease in the base flow during the low-flow period (May-November) and an increase in the storm runoff during the high-flow period (December to April). It can be concluded that climatic variability and land use change are the most important factors affecting the (changes in the) hydrologic regime of the Minab catchment's. For a flood return period of more than 10 years, (high) rainfall intensity as a climatic factor is considered dominant. For a return period of less than 10 years in combination with a low flow period, land use change is the dominant factor determining the flow regime. An active management strategy aimed at the conservation and regeneration of the natural vegetation is recommended, in order to improve the distribution of water throughout the entire Minab catchment's, during both dry and wet periods.
Keywords: Land cover change, climatic variability, catchment hydrology, remote sensing, GIS
posted by khosroshahi | 10:39 PM
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