ارزیابی اثرهای تغییراقلیم و کاربری‌های اراضی بر ذخایر برفی و خدمات اکوسیستمی در حوضه آبخیز کرج

این پژوهش با هدف ارزیابی محیط زیستی اثر تغییرات آب و هوایی و کاربری اراضی بر ذخایر برفی و خدمات اکوسیستمی در حوضه آبخیز کرج انجام شد. ابتدا تصاویر لندست سنجنده های tm، etm و oli برای سال های 2000، 2005، 2010، 2015 و 2020 تهیه شد. شاخص ndsi بر روی تصاویر اعمال شد و پهنه های برفی استخراج گردید. نقشه های کاربری اراضی برای سال های 1990، 2000 و 2020 با اعمال الگوریتم طبقه بندی ماشین بردار پشتیبان (svm) بر روی تصاویر لندست به دست آمد. برای بررسی نقش تغییر اقلیم و تغییرات کاربری اراضی بر خدمات اکوسیستمی منطقه در بخش ترسیب کربن و تخریب سرزمین از نرم افزار invest و arcgis pro استفاده شد. نتایج نشان داد که در بیست سال اخیر (2000-2020) حدود 6312 هکتار از ذخایر برفی حوضه آبخیز کرج ذوب شده و به صورت رواناب از حوضه خارج شده است. از سال 1990 تا 2020، حدود 14.640 هکتار از مراتع سرد کوهستانی کاسته شده است، اما حدود 1.189 هکتار بر وسعت باغ شهری ها افزوده شده است. نتایج کمّی سازی خدمات اکوسیستمی نشان داد که کیفیت بد خدمات اکوسیستمی در سال 2020 بیش از 15 هزار هکتار افزایش یافته است و همین مقدار از کیفیت خوب اکوسیستم کاسته شده است که این تغییرات مربوط به تبدیل اراضی مرتعی و پوشش گیاهی بوته ای به باغ شهری ها است. همچنین حدود 113.313 تُن ترسیب کربن در طی 30 سال گذشته کاهش یافته است که دلیل اصلی آن تبدیل کاربری مرتعی و درختزار و به باغ شهری ها است. پس می توان نتیجه گرفت که تبدیل مراتع و درختزارها در دره های رودخانه کرج به باغ شهری های انسان ساخت و مراگز گردشگری، باعث کاهش خدمات اکوسیستمی حوضه آبخیز کرج در 30 سال گذشته شده است.

evaluation of the effects of climate change and land use on snow reserves and ecosystem services in the karaj watershed

1- introductionthe watershed of the karaj river, which is located in the southern of the middle alborz mountain range in the north of the city of karaj, is the source of water supply for the urban settlements of karaj, tehran and satellite towns, industrial towns, agriculture and environmental ecosystems of the regions. it is downstream. amir kabir dam, which is one of the reservoirs for drinking water and supplying electricity to the megacities of karaj and tehran, is built on the karaj river. if there is a change in the amount of water, snow storage or its land cover, it can severely affect the life of the downstream environmental and human ecosystems. in order to deal with these conditions, the situation of the karaj watershed’s snow reserves should be known. the land use map should be prepared with proper accuracy so that the ecosystem services that exist in this basin can be identified based on it. if the climatic condition and ecosystem services are estimated, a suitable strategic strategy for watershed management can be formulated. therefore, the main goal of this current research is to evaluate and understand the changes in snow deposits and land use in the karaj watershed in the last 30 years and the effect of these changes on the ecosystem services of this basin.2- methodologyby implementing the support vector machine (svm) algorithm, the land use map for 1990 and 2020 was prepared. considering the mountainous nature of the basin and the absence of urban or rural settlements, land use was classified into four classes: cold mountain pastures, water area, snow area and gardens. after preparing basic maps of land use and snow cover, the changes in ecosystem services provided by the karaj watershed were quantified and compared in 1990 and 2020. invest software was used to calculate ecosystem services and the obtained maps were drawn in arcgis pro software.3- results the results showed that in the last 20 years (2000-2020), about 6312 hectares of snow deposits in the karaj watershed have melted and left the basin as runoff. from 1990 to 2020, about 14,640 hectares of cold mountain pastures have been reduced, but about 1,189 hectares have been added to the area of urban gardens. the results of the quantification of ecosystem services showed that the bad quality of ecosystem services increased by more than 15 thousand hectares in 2020, and the same amount of good quality of the ecosystem was reduced, that these changes are related to the conversion of pasture lands and bush vegetation to it is an urban garden. also, about 113,313 tons of carbon deposition has been reduced over the past 30 years, the main reason for which is the conversion of pastures and groves to urban gardens. therefore, it can be concluded that the conversion of pastures and groves in the valleys of the karaj river into man-made urban gardens and tourist attractions has reduced the ecosystem services of the karaj watershed in the past 30 years.4- discussion & conclusionsthe reduction of pastures, bushes and cold woodlands in the alborz mountains in the karaj watershed and the increase of urban gardens and tourist centers lead to a decrease in the quality of the ecosystem and also to a decrease in the amount of carbon sequestered by natural pastures and groves. in such a way that during the last 30 years, about 104,826 tons of carbon sequestration has been reduced, which is caused by these land use changes. on the other hand, the good quality of ecosystems has also decreased by about 15,167 hectares and has turned into bad ecosystem quality. therefore, it can be concluded that the land use changes and climate changes that happened during the last 30 years lead to a decrease in the services that the environmental ecosystems of the karaj watershed can provide and cause environmental sustainability.