پايش خشكسالي كشاورزي استان مركزي با استفاده از شاخص هاي VHI و PDSI

Monitoring of Agricultural Drought in Markazi Province using VHI and PDSI Indices

خشكسالي از جمله بلاياي طبيعي و ادامه ­ي آن درسطح وسيع باعث نابودي حيات مي­شود. اين پديده در علوم مختلف به چند دسته كشاورزي، هواشناسي، هيدرولوژي ، توان طبيعي دسته بندي مي­شود. خشكسالي محصولات كشاورزي باعث آسيب زدن به اقتصاد، شرايط اجتماعي، محصولات كشاورزي و در نتيجه امنيت غذايي مي­شود لذا پايش آن امري ضروري است. امروزه براي بررسي خشكسالي كشاورزي از روش­هايي همچون دوركاوي و استفاده از داده­هاي ماهواره ­اي دركنار داده­هاي هواشناسي يا شاخص­ هاي خشكسالي استفاده مي­شود. در اين تحقيق از داده­هاي سنجنده­ ي ماديس ماهواره ­ي ترا، نقشه ­يLST ، شاخص NDVIو از داده­ هاي سنجنده­ ي سنتينل2، نقشه ­ي شاخص خشكسالي PDSI استان مركزي در سال­هاي 1388 ، 1393و 1398 تهيه مي­شود. ميزان بارندگي از سنجنده­ ي هواشناسي GPM و ميزان رطوبت سطح و زير سطح خاك، از داده­هاي سنجنده ­ي SMAP در بازه­ ي 1388 تا 1398 براي شهرستان­ هاي شارند، كميجان و تفرش، به عنوان سه منطقه نمونه با شدت خشكسالي متفاوت جهت تحليل شدت خشكسالي استخراج شد. پس از تهيه داده­هاي مورد نياز، از LST شاخص TCI، از شاخص NDVI شاخص VCI و در نهايت با استفاده از TCI, VCI، شاخص VHI استان مركزي در1388، 1393 و 1398 ، تهيه مي­شود. با استفاده از نقشه­ شاخص­ها و مقادير آنها مي­توان در سال­هاي مختلف وضعيت پوشش گياهي و محصولات كشاورزي به همراه شدت خشكسالي نقاط مختلف استان را مشاهده نمود. پس از تهيه نقشه­ شاخص­ها، اثر تغييرات شاخص­هاي LST وNDVI بر روي شاخص VHI و اثر شاخص VHI،SM ،SSM و ميزان بارش بر روي شاخص PDSI بررسي مي­شود. نتايج نشان مي­دهد كه شاخص VHI با شاخص LST رابطه­ ي معكوس و با شاخص NDVI و PDSI رابطه­ ي مستقيم دارد. براساس يافته­ ها جنوب غرب استان كمترين شدت خشكسالي و شرق استان بالاترين شدت خشكسالي را داشته است. در مقايسه با ساير پژوهش ­هاي انجام شده در اين زمينه، در اين تحقيق پايش شدت خشكسالي كشاورزي منطقه مطالعاتي با استفاده از شاخص خشكسالي PDSI انجام شده است.

One of the natural disasters of all is drought. Drought has long been one of the problems of Iran and has always been mentioned as a serious threat to the country. Drought is one of the natural and repetitive features of the climate and part of the climate that cannot be observed without a specific limit of occurrence and impact using high-speed ground station information. Drought rate is divided into severe, mild, moderate drought and long-term drought and short-term drought based on time components. Drought has had effects on land degradation, forest fires, reduced air and water quality, and reduced agricultural production. Frequent droughts have been a concern for many years, and on a global scale, in recent decades, especially in arid and semi-arid regions, the frequency, severity and duration of droughts have increased significantly. Drought according to different definitions in each area is divided into four main categories, including meteorological drought, agricultural drought, hydrological drought and socio-economic drought. In meteorology, drought, or in other words dry period, is the reduction of loss in a period of time compared to the average amount of rainfall in that period or the amount of long-term rainfall in the same period. Of course, if this amount of rainfall does not meet the needs such as economic and social needs. The duration or period of drought varies according to the climate of each region and depends on the location and time. In Iran, the drought period is approximately equal to the crop year. The severity of drought also varies in each climate and country. The same amount of rainfall in one country may be considered drought, while in another country, the same amount of rainfall does not indicate drought. Agricultural drought damages the economy, social conditions, agricultural products and consequently food security, so monitoring it is essential. For this purpose, agricultural drought in Markazi province has been studied. One of the factors affecting agricultural drought, soil moisture and plant evapotranspiration as a cause of water loss is the difference between the available water and its wastage. Therefore, to measure drought, an indicator that shows evapotranspiration is needed. In this research, RWDI index is used as an indicator of drought based on evapotranspiration. To obtain this index, one must first obtain the actual evapotranspiration and potential. Due to the advantages of remote sensing methods compared to traditional methods, remote sensing methods based on energy balance and SEBAL2 image processing model as well as Landsat 8 images, in dry and wet seasons, along with meteorological data to obtain heat flux Hidden, which depends on the parameters of soil heat flux, tangible heat flux and net radiation flux, is used. Using latent heat, instantaneous evapotranspiration is calculated daily and using the Penman 3 method, reference evapotranspiration is calculated. Potential method of Taylor 4, evapotranspiration and potential transpiration are obtained, and as a result, after calculating the actual evapotranspiration, the RWDI index is prepared, which shows the water shortage and the severity of agricultural drought. The results show that the values ​​of evapotranspiration are obtained with acceptable accuracy. Meteorological stations are obtained in REF-ET software. In addition, based on the results of the water deficit index, the values ​​of this index are expected to be higher in dry seasons than in wet seasons.