بررسي روند مكاني و زماني بارش در حوضه خزر با استفاده از داده‌هاي مركز اقليم‌شناسي بارش جهان

Analysis of the spatial and temporal trend in precipitation on Caspian basin using GPCC data

ﺑﺎرش در ﺣﻮﺿﻪ ﺧﺰر ﺑﻪﻋﻨﻮان ﻣﻬﻤﺘﺮﯾﻦ ﺳﻨﺠﻪ اﻗﻠﯿﻤﯽ ﺗﻮزﯾﻊ زﻣﺎﻧﯽ و ﻣﮑﺎﻧﯽ ﺧﺎص و ﭘﯿﭽﯿﺪهاي دارد. ﺑﺪﯾﻦ دﻟﯿﻞ، آﮔﺎﻫﯽ از ﺗﻐﯿﯿﺮات ﻣﮑﺎﻧﯽ و زﻣﺎﻧﯽ آن در اﯾﻦ ﺣﻮﺿﻪ آﺑﯽ از اﻫﻤﯿﺖ وﯾﮋهاي ﺑﺮﺧﻮردار اﺳﺖ. زﯾﺮا، ﺗﻐﯿﯿﺮات آن ﻣﯽﺗﻮاﻧﺪ ﭘﯿﺎﻣﺪﻫﺎي ﻣﺨﺘﻠﻒ زﯾﺴﺖﻣﺤﯿﻄﯽ، اﻗﺘﺼﺎدي و اﺟﺘﻤﺎﻋﯽ ﺑﻪ ﻫﻤﺮاه داﺷﺘﻪ ﺑﺎﺷﺪ. ﻫﺪف از اﯾﻦ ﭘﮋوﻫﺶ، واﮐﺎوي ﺗﻐﯿﯿﺮات ﻣﮑﺎﻧﯽ و زﻣﺎﻧﯽ ﺑﺎرش در ﺣﻮﺿﻪ ﺧﺰر اﺳﺖ. ﺑﺪﯾﻦ ﻣﻨﻈﻮر، داده ﻫﺎي ﻣﺎﻫﺎﻧﻪ ﺑﺎرش از ﺗﺎرﻧﻤﺎي ﻣﺮﮐﺰ آب و ﻫﻮاﺷﻨﺎﺳﯽ ﺑﺎرش ﺟﻬﺎﻧﯽ )GPCC( ﺑﺎ ﺗﻮان ﺗﻔﮑﯿﮏ 0/5 در 0/5 درﺟﻪ ﻗﻮﺳﯽ در ﯾﮏ دوره آﻣﺎري 63 ﺳﺎﻟﻪ )1951 ﺗﺎ 2013( اﺧﺬ ﺷﺪ. ﺑﺮاي ارزﯾﺎﺑﯽ ﺗﻐﯿﯿﺮات ﻣﮑﺎﻧﯽ و زﻣﺎﻧﯽ ﺑﺎرش، از داده ﻫﺎي اﺳﺘﺨﺮاج ﺷﺪه از اﯾﻦ ﭘﺎﯾﮕﺎه داده ﺑﺎرﺷﯽ ﻣﯿﺎﻧﮕﯿﻦ ﺳﺎﻻﻧﻪ، ﻓﺼﻠﯽ و ﻣﺎﻫﺎﻧﻪ ﺗﻬﯿﻪ ﺷﺪ. آزﻣﻮن ﻧﺎﭘﺎراﻣﺘﺮي ﻣﻦ-ﮐﻨﺪال ﺑﺎ اﺣﺘﻤﺎل 95 درﺻﺪ ﺑﺮ روي دادهﻫﺎي ﻣﺎﻫﺎﻧﻪ، ﻓﺼﻠﯽ و ﺳﺎﻻﻧﻪ اﻋﻤﺎل و ﺑﺎ اﺳﺘﻔﺎده از ﻧﺮم اﻓﺰار ArcGIS، ﻧﻘﺸﻪ ﻫﺎي 17ﮔﺎﻧﻪ روﻧﺪ ﻣﮑﺎﻧﯽ ﺑﺎرش در ﺳﻄﺢ ﺣﻮﺿﻪ ﺗﺮﺳﯿﻢ ﺷﺪ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ ﺑﺎرش در ﻣﺎهﻫﺎي ﻣﺎرس و آورﯾﻞ در ﭘﻬﻨﻪﻫﺎي ﻏﺮﺑﯽ، ﺷﺮﻗﯽ و ﺟﻨﻮب ﻏﺮﺑﯽ ﺣﻮﺿﻪ ﺧﺰر روﻧﺪ ﮐﺎﻫﺸﯽ ﻣﻌﻨﺎداري ﺑﺎ اﺣﺘﻤﺎل 95 درﺻﺪ دارد. در ﺑﺎزه زﻣﺎﻧﯽ ﻓﺼﻠﯽ، ﺑﺎرش ﺗﻨﻬﺎ در ﻓﺼﻮل ﺑﻬﺎر و ﭘﺎﯾﯿﺰ روﻧﺪي ﻣﻌﻨﯽدار و ﮐﺎﻫﺸﯽ در ﺑﺨﺶ ﻏﺮﺑﯽ ﺣﻮﺿﻪ دارد، اﯾﻦ در ﺣﺎﻟﯽ اﺳﺖ ﮐﻪ در ﻓﺼﻮل ﺗﺎﺑﺴﺘﺎن و زﻣﺴﺘﺎن، ﻓﺮض وﺟﻮد روﻧﺪ ﺗﺄﯾﯿﺪ ﻧﺸﺪ. ﺗﺤﻠﯿﻞ ﺗﻐﯿﯿﺮات ﻣﮑﺎﻧﯽ ﺑﺎرش ﺳﺎﻻﻧﻪ ﻧﯿﺰ ﻧﺸﺎن از روﻧﺪ ﮐﺎﻫﺸﯽ ﻣﻌﻨﯽدار در ﭘﻬﻨﻪ ﻏﺮﺑﯽ ﺣﻮﺿﻪ دارد. واﮐﺎوي ﺗﻐﯿﯿﺮات ﺑﺎرش ﺣﻮﺿﻪ ﺧﺰر در ﺳﺮي ﻫﺎي زﻣﺎﻧﯽ ﻣﺎﻫﺎﻧﻪ ﻧﯿﺰ ﺣﮑﺎﯾﺖ از روﻧﺪ ﮐﺎﻫﺸﯽ ﻣﻌﻨﯽدار ﺑﺎ اﺣﺘﻤﺎل 95 درﺻﺪ در ﻣﺎه ﻣﺎرس در اﯾﻦ ﺣﻮﺿﻪ دارد.

In this research, for analysis the spatial- temporal trend of precipitation in Caspian basin, the monthly data of GPCC data base in the spatial resolution of 0.5°×0.5° during 63 years period(1951- 2013) have been used. In order to analyze of the spatial- temporal trend of precipitation, the mean of annual, seasonal and monthly amounts of precipitation were prepared and then by applying Mann-Kendall nonparametric test at 0.95 level of significance, 17 maps precipitation spatial trend were produced in GIS. To examine the temporal trend of precipitation, first 17 graphs were prepared using the weighted amount of precipitation and then the trend was evaluated using Mann-Kendall nonparametric test at 0.95 level of significance. The evaluation of monthly precipitation spatial trend maps indicated a significant downward trend at 0.95 level of significance in March and April on the western, eastern and southwest regions of Caspian basin. Only in spring and autumn there have been a significant downward trend and in none of the other seasons no meaningful trend was detected. Also, the analysis of yearly precipitation spatial trend illustrated a significant downward trend on western region. The analysis of precipitation revealed significant downward trend on monthly time series at the 0.95 level of significance in March on Caspian basin.