جستجوی مقالات مرتبط با کلیدواژه "حوضه دریاچه نمک" در نشریات گروه "آبخیزداری، بیابان، محیط زیست، مرتع"

In the present paper, trends of rainfall, runoff and temperature in the Kordan sub-basin which is one of the sub-basins of Qazvin basin were investigated for period of 1966-95. This sub-basin with 360 km2 area is located in the north eastern part of Qazvin basin with a different range of elevation from 1410m to 4108m. Results show although there is not any change in the trend of annual rainfall, but a significant increase and decrease in total amount of precipitation in the second half of year (cold months) and in the first half of year (warm months) and increase in the monthly temperature in most of months were observed. Also trend of moving average of ratio runoff/rainfall (coefficient of runoff) shows significantly a sharp increase annually and also for seasons of spring and autumn. A comparison for coefficient of runoff between first and third decade of period shows different amounts of increase annually and also for seasons of spring and autumn as 58.9%, 12.9% and 5.1% respectively. Increasing of coefficient of runoff in spring is related to general increase of temperature and also precipitation increase in winter season. Increasing of coefficient of runoff in autumn is related to precipitation increase in this season and also occurrence of mismanagement in plant, soil and water resources. Therefore the volume of runoff in this sub-basin which is evacuated and wasted more than before, reaches to 9.4 million m3 per year.

Of the many Climatic events that influence earth’s environmental fabric‚ drought is perhaps the one that is most linked with desertification(WMO‚1997).This Investigation is an effort for assessment of acceptability about many of Climatic current Drought Indices in reagent and sample stations of Salt Lake Basin of Iran. These drought indices which are used in world active systems, are Percent of normal precipitation Index PNI, Deciles of precipitation Index DPI, Standardized precipitation Index SPI, and Z Score Index ZSI.The above mentioned indices were calculated first by average of monthly precipitation data for a 44 years period from 1957 to 2000 relate to 34 synoptic and climatological stations in their common time scales. Based on obtained results from one hypotheses, DPI and SPI indices in the contemporary with minimum occurrence, showed, extremely drought in the studied stations. These acceptability of indices in more than of other indices and according of this investigation,DPI index sit on the first place, SPI sit on the second place, ZSI index sit on the third place, and finally PNI Index, sit on the forth place. In next stage the Standardized Precipitation Index SPI, based on precipitation values from 34 monitoring stations around the Salt Lake Basin of Iran, is computed monthly and was performanced for climatic interpret and characteristic include assess drought relative frequency, intensity, expand and duration and calculated return period of the most intense drought and according to the point stations data, drew intense map. This investigation indicate the most intense drought in Salt Lake Basin of Iran belong to Hamadan(Nozheh) and the longest drought duration in Avaj ‚Dooshantappeh‚ and Kashan Stations with the highest relative frequency digit of drought (38/6%) and the lowest relative frequency digit of drought (18/1%) belong to Golpayegan. The most of severe year has occurred in 1973 and 1967 in 44 years period.