مطالعه خشك‌سالي با استفاده از شاخص‌هاي هواشناسي و داده‌هاي سنجش‌ازدور (استان آذربايجان غربي)

Study of drought using meteorological and remote sensing data (Azarbaijan province)

در سال­هاي اخير خشك ­سالي تأثير مخربي در بيشتر بخش­ هاي اكولوژي، مديريت منابع آب، و فرآيند­هاي زيست­ محيطي برجا گذاشته است. در اين تحقيق جهت ارزيابي خشك­ سالي از اطلاعات حاصله از تصاوير سنجنده MODIS در استخراج شاخص NDVI و DVI استفاده شده ­است. هدف از اين تحقيق بررسي خشك ­سالي­ هاي هواشناسي در منطقه با استفاده از دو شاخص هواشناسي SPI و ZSI به‌صورت دوره­هاي ماهانه و همچنين بررسي رابطه بين شاخص پوشش گياهي با خشك ­سالي­هاي هواشناسي مي­باشد. درصد كل پوشش در منطقه مورد مطالعه براي سال­هاي ترسالي 1383، 1385،1390 و 1393 به‌ترتيب 85/19، 5/19، 6/19 و 5/19 درصد بوده و در سال­هاي خشك‌سالي 1384، 1387، 1389 به‌ترتيب 71/18، 7/18 و 19 درصد محاسبه شد. بيشترين همبستگي بين شاخص NDVI و DVIبا دوره­هاي كوتاه‌مدت (1، 2 و 3 ماهه) شاخص ­هاي SPI و ZSI وجود دارد. همچنين همبستگي معني‌دار بين شاخص­ هاي پوشش گياهي و دوره‌هاي بلندمدت شاخص ­هاي هواشناسي مشاهده نشد. به‌طوركلي بيشترين ميزان همبستگي در طول دوره آماري بين شاخص­ هاي SPI و NDVI و همچنين در سالي كه شرايط خشك‌سالي نرمال گزارش شد، به دست آمد. علاوه بر اين تعيين روند شاخص ­هاي مورد مطالعه با استفاده از روش من-كندال نشان از وجود روند نزولي در همه شاخص­ ها و افزايش خشك‌سالي و كاهش پوشش گياهي در طول دوره آماري مي­باشد.

In recent years, drought has created a destructive impact on the ecology, water resources management, and ecological processes. In this context, appropriate and appropriate method for predicting and monitoring the drought could have a significant impact in neutralizing the effect of this natural phenomenon. In this research, drought monitoring and evaluation of data from MODIS images were used in the extraction of NDVI and DVI indices. The study area of West Azarbaijan province is one of the northwest provinces of the country. In this study, images of meteorological index of drought or wet year have been used. ArcGIS 9.3 has been used to prepare and perform the necessary corrections on the images, as well as to prepare the vegetation cover index (NDVI) and vegetation difference index (DVI) using ENVI 4.5 software, to classify the results and output in the formg images. The aim of this study was to evaluate meteorological droughts using SPI and ZSI as monthly intervals and also determine the correlation between vegetation and meteorological droughts that happened in this area. The results of SPI and ZSI indices indicate that in the first three months of the year, the vegetation is moderate in the prevailing region, and in the second quarter of the year, the maps indicate weak and uncoated vegetation, because the rainfall is very limited in this time. On the other hand, in these months of the year, overgrazing has caused plant degradation. Vegetation in the first three months of the year seems to have had more favorable conditions due to the melting of snow and winter and autumn rainfall of the previous year. Percentage of vegetation coverage in the study area for the wet years 1383, 1385, 1390 and 1393, was respectively reported as 19.85%, 19.5%, 19.6% and 19.5% and also in the drought years 1384, 1387, and 1389 it was calculated as 18.71%, 18.7% and 19% respectively. The results of SPI and ZSI indices indicate that in the first three months of the year, the vegetation is moderate in the prevailing region, and in the second quarter of the year, the maps indicate weak and uncoated vegetation because the rainfall is very limited at this time. On the other hand, in these months of the year, overgrazing has caused plant degradation. Should be cautious about further action beacause One NDVI index is correlated with meteorological drought indices SPI and ZSI which is varied with respect to the short-term and long-term interval respectively. The result confirmed that NDVI and SPI indices were appropriate for monitoring and assessment of drought. The highest correlation values between NDVI and DVI was observed for short term intervals of SPI and ZSI (1, 2 and 3 months). Generally the highest correlation values during the statistical period between NDVI and SPI was obtained as well as in the year when normal drought conditions were reported. In addition, the determination of trends of the indices using the Man Kendall test indicated that there exist a downward trend in all indices and there was an increase in drought and vegetation decline during the statistical period.