Setareh Bagheri; Reza Tamartash; Mohammad Jafari; Mohammad Reza Tatian; Arash Malekian
Abstract
Plain ecosystem is highly vulnerable to environmental changes, and drought is the most famous ecosystem change driver that is difficult to identify after its occurrence. In this research, to study the slope of vegetation changes against drought, the NDVI index of MODIS images and the SPI index from 2001 ...
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Plain ecosystem is highly vulnerable to environmental changes, and drought is the most famous ecosystem change driver that is difficult to identify after its occurrence. In this research, to study the slope of vegetation changes against drought, the NDVI index of MODIS images and the SPI index from 2001 to 2016 were used and the map of vegetation changes against drought with five drought stress classes included very low classes, Low, moderate, high and very high, so that a suitable assessment of the drought can be made at specified time scales. The results of slope pattern of spatial change of vegetation against drought showed that across the plain vegetation changes have declined, and from east to west of Qazvin plain, the slope of vegetation changes and land susceptibility to drought have been reduced. So that the most percentage of area in a one-month drought related to the drought class is very low, but in droughts of 3, 6, 9, 12, 24 and 48 months, the highest percent of the area belonged to moderate and high drought classes. The results of this study, the determination of the level of vegetation changes in against drought in the past years and prediction of these changes in the future years, can be used in the planning and optimal use of resources, control changes in the future.
Khaled Osati; Hamed Joneidi; Nahid Azizi
Abstract
Prediction of rangeland species forage yield is one of the most effective tools for planning and policymaking of natural resources in each country. Climate variables (precipitation and temperature) play an important role in forecasting rangeland species production. In the present study, the forages yields ...
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Prediction of rangeland species forage yield is one of the most effective tools for planning and policymaking of natural resources in each country. Climate variables (precipitation and temperature) play an important role in forecasting rangeland species production. In the present study, the forages yields of some typical species in Ghoosheh rangeland, Semnan, measured using cutting and weighing method. It was evaluated in 30 plots with an area of two square meter, distributed along with two transect lines, for a 10-year period (water year 2005-2006 to 2014-2015), to determine the effects of drought on the forages yield of typical species in the studied areas. In the next step, several drought indices were calculated. The relationship between forages yield of rangeland species and drought indices values investigated to model forages production of study areas via drought indices. According to the values of drought indices SIAP, PNPI and Z-Score, several drought and wet-year periods occurred during the assessed 10-year. The relationship between forages production and drought indices confirmed that the best simple linear regression model for estimating total forages production of studied area was introduced by SIAP and Z-Score indices (RRMSE = 0.1) explaining 53% of production changes at 95% confidence level. The effects of drought and wet-year periods varied among different species so as to the annual production varied greatly for annual species (between 1 and 11% of total annual forages yield) and slightly for perennials and shrubs.
