Economic valuation of water production service in forest ecosystems (case study: Darabkola watershed)

One of the most important causes of the destruction and decline of natural ecosystems is the lack of a market to determine the value of services produced by these ecosystems, and as a result, consider these services free. One of the most valuable services provided by ecosystems is the production of fresh water which in the present study, a model has been presented for achieving the spatial distribution of service value of water production ecosystem in Darabkola watershed that is located in Mazandaran Province.

In this study, was used the water yield model in InVEST to quantify the water production service. In the model, the water production was calculated the based on the Budyko curve, which in fact determines the amount of water running off each pixel of land as the total precipitation minus evapotranspiration. The required data include maps of land use and land cover, average annual precipitation and potential evapotranspiration, soil depth, plant available water content, boundary of watersheds and sub-watersheds as well as a biophysical table. In order to evaluate this ecosystem service has been valued with the replacement cost and thus it has been possible to obtain a spatial distribution map of the value of water production ecosystem service in the study area.

According to the calculations done by the model in whole Darabkola watershed, annually 43094152  of water is produced. The results of different land uses indicated that the highest amount of runoff in land uses is in man-made land use equal to 3743.76  and followed by agriculture and garden land uses with values of 3601.34  and 3592.18  had the highest water production, respectively. Also, the lowest runoff was related to the uses of semi-dense forest and dense forest with values of 2960.82  and 2602.19 , which indicates that the presence of the canopy of forest trees and their spatial distribution has an important effect on increasing water penetration in the soil and reducing runoff production. The study area is classified into four different classes of value in terms of economic value of water ecosystem services. These classes differ from a minimum of 24 - 29 million Rials to a maximum of 39 - 43 million Rials per hectare.

The results of this study showed that Although InVEST model needs available and relatively simple data but it has high efficiency and we can use it for mapping ecosystem services and decision making. Also, using the quantitative results obtained from the implementation of the InVEST model, it was possible to show the spatial distribution of the value of ecosystem services in the study area. The results of this section showed that attention to the spatial dimensions is very important in determining the value of water production service, because the change in spatial characteristics will greatly affect the value of water production service.