خلاصة:
Drought is a normal, recurring feature of climate phenomena; it may occur virtually in all climatic regions. The
effects of drought accumulate slowly and its impacts are spread over a larger geographical area than other natural
hazards. Drought is a natural hazard originating from a deficiency of precipitation that result in a water shortage for
some activities or some groups and is often associated with other climatic factors such as high temperatures, high
winds and low relative humidity that can aggravate the severity of the event. Iran is frequently affected by recurring
droughts. In this research the Qom province with an area 11500 km2 that located in an arid and semi arid region of
Iran was selected. Eighth site of rangeland were chosen that represented rangeland situation in the study area. In
these sites relative factors such as plant cover , density, yield, regeneration ,land cover were measured in 60 plots
with 2 m2 area along the 4 transect with 400 m along. Rangeland yield was measured with the cutting and weighting
method in a quarter of plots, and the total yield in each site was obtained from the regression models between plant
cover and species yield. Data series were cumulated for 9 years (1998-2006). Palmer drought severity index (PDSI)
carried out in this study. The objective of this study is to performance of the PDSI to assessment of drought in the
rangeland of the Qom. The analysis of results indicated that each site growth season is different from another. The
rangeland yield is not related to the annual rainfall, but the best relationship was between rainfall in growth season
and range yield. Also the study showed that the highest frequency of significant models is related to March-July
period.
ملخص الجهاز:
Assessment of the Palmer drought severity index in arid and semi arid rangeland: (Case study: Qom province, Iran) M.
The objective of this study is to performance of the PDSI to assessment of drought in the rangeland of the Qom. The analysis of results indicated that each site growth season is different from another.
According to Wilhite and Glantz (1985) classification, four categories of droughts could be identified: 1) meteorological drought which is the negative departure of precipitation from the normal precipitation over a period of time, 2) hydrological drought which is the deficiency in surface and subsurface water supplies, 3) agricultural drought which is shortage of soil moisture that is necessary for the development of a particular crop at a specific time and 4) socio-economic drought which is referred to the failure of water resources to meet the water demands.
Drought is a natural hazard originating from a deficiency of precipitation those results in a water shortage for some activities or some groups and is often associated with other climatic factors such as high temperatures, high winds and low relative humidity that can aggravate the severity of the event.
Drought is a natural hazard originating from a deficiency of precipitation those results in a water shortage for some activities or some groups and is often associated with other climatic factors such as high temperatures, high winds and low relative humidity that can aggravate the severity of the event.
For this purpose Palmer drought severity index was calculated for 20 years period (1986-2006), and then the results compared with the rangeland yield.