Conversion trends of rangelands to dry farming and its effects on erosion and sediment yield in Kardeh drainage basin

Converting rangelands to arable land such as dry farming is widely practiced in many places in Iran. This activity could possibly contribute to the increase in downstream sedimentation. The effects of this activity on downstream watersheds are not well documented for many strategic areas in the country. One such area which is proposed for this study is the Kardeh drainage basin, located in the north east of Iran, having a catchment area of 570.9 km2. In this study, an attempt was made to quantify the changes in land use, and the sediment yield of the basin, and to identify significant contributing factors that could possibly contribute to the increased downstream sedimentation between the years of 1970 and 2007. Available satellite images and aerial photos were analyzed for the extent of land use changes and an empirical model, Erosion Potential Method (EPM) was validated and applied to quantify the annual total sediment yield of the basin. Step-wise multiple regressions were used to justify that the changes in sediment yield is due to the increased dry farming activities. The results showed a drastic change in land use between these periods where dry farming area has remarkably increased to 91%, while there was a reduction in rangeland area of about 13%. The effect of increased dry farming activities is reflected on the two fold increase in annual total sediment yield of the basin. Statistically, about 95% of the changes in sediment yield is due to the effect of increased dry land farming area in the basin (R2= 0.95, α < 0.05)