A GIS-based method has been applied for the determination of soil erosion and sediment yield in a small watershed in Mun River basin, Thailand. The method involves spatial disintegration of the catchment into homogenous grid cells to capture the catchment heterogeneity. The gross soil erosion in each cell was calculated using Universal Soil Loss Equation (USLE) by carefully determining its various parameters. The concept of sediment delivery ratio is used to route surface erosion from each of the discritized cells to the catchment outlet. The process of sediment delivery from grid cells to the catchment outlet is represented by the topographical characteristics of the cells. The effect of DEM resolution on sediment yield is analyzed using two different resolutions of DEM. The spatial discretization of the catchment and derivation of the physical parameters related to erosion in the cell are performed through GIS techniques.
Global groundwater assessments rank Iran among countries with the highest groundwater depletion rate using coarse spatial scales that hinder detection of regional imbalances between renewable groundwater supply and human withdrawals. Herein, we use in situ data from 12,230 piezometers, 14,856 observation wells, and groundwater extraction points to provide ground-based evidence about Iran’s widespread groundwater depletion and salinity problems. While the number of groundwater extraction points increased by 84.9% from 546,000 in 2002 to over a million in 2015, the annual groundwater withdrawal decreased by 18% (from 74.6 to 61.3 km3/y) primarily due to physical limits to fresh groundwater resources (i.e., depletion and/or salinization). On average, withdrawing 5.4 km3/y of nonrenewable water caused groundwater tables to decline 10 to 100 cm/y in different regions, averaging 49 cm/y across the country. This caused elevated annual average electrical conductivity (EC) of groundwater in vast arid/semiarid areas of central and eastern Iran (16 out of 30 subbasins), indicating “very high salinity hazard” for irrigation water. The annual average EC values were generally lower in the wetter northern and western regions, where groundwater EC improvements were detected in rare cases. Our results based on high-resolution groundwater measurements reveal alarming water security threats associated with declining fresh groundwater quantity and quality due to many years of unsustainable use. Our analysis offers insights into the environmental implications and limitations of water-intensive development plans that other water-scarce countries might adopt.
The anthropogenic impacts of development and frequent droughts have limited Iran's water availability. This has major implications for Iran's agricultural sector which is responsible for about 90% of water consumption at the national scale. This study investigates if declining water availability impacted agriculture in Iran. Using the Mann-Kendall and Sen's slope estimator methods, we explored the changes in Iran's agricultural production and area during the 1981-2013 period. Despite decreasing water availability during this period, irrigated agricultural production and area continuously increased. This unsustainable agricultural development, which would have been impossible without the overabstraction of surface and ground water resources, has major long-term water, food, environmental, and human security implications for Iran. Plain Language Summary Given the heavy reliance of the agricultural sector on water availability, it is important to examine if Iran's agriculture has been impacted by water availability changes in recent decades. The investigation of the long-term impacts of natural water availability changes on agricultural activities in the country during the 1981-2013 period revealed that the agricultural sector in Iran continued to expand regardless of decreasing water availability in the country. This expansion was facilitated by the excessive use of nonrenewable water resources which has significant environmental and socioeconomic implications.
This study aims at understanding the impacts of projected climate change on the hydrological processes within the Maumee River watershed (16 395 km2) lying in the Lake Erie Basin using soil and water assessment tool (SWAT). The model was calibrated and validated for a baseline time‐period of 1995–2005. Downscaled ensemble projected temperature and precipitation data from three general circulation models (GCMs) was then used to assess future flow, sediment, and nutrient loading in the watershed for mid‐century (2045–2055) and late‐century (2089–2099) time periods. Compared to the baseline, a 2.9°C rise in the annual average temperature along with a 3.2% fall in the annual precipitation in the mid‐century time‐period is projected to reduce annual flow volumes, and suspended solids (SS), total phosphorus (TP), nitrate (NO3) loads by 8.5, 10.4, 8.5, and 9.9%, respectively. Similarly, for the late‐century a 4.3°C rise in the annual average temperature along with a 5.6% rise in the annual precipitation is projected to increase annual flow volumes, and SS, TP, NO3 loads by 9.7, 19.6, 3.5, and 6.8%, respectively. Temporal shifts in climatic conditions were also projected for both the future time‐periods with higher temperatures throughout the year along with wetter winters and drier summers. Implications of these changes would include the need for an increased focus on pollutant loadings for total maximum daily load guidelines and possible lengthening of crop growing cycles.
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