Abstract:Extensive studies on hydrological responses to forest change have been published for centuries, yet partitioning the hydrological effects of forest change, climate variability and other factors in a large watershed remains a challenge. In this study, we developed a single watershed approach combining the modified double mass curve (MDMC) and the time series multivariate autoregressive integrated moving average model (ARIMAX) to separate the impact of forest change, climate variability and other factors on dry season runoff variation in two large watersheds in China. The Zagunao watershed was examined for the deforestation effect, while the Meijiang watershed was examined to study the hydrological impact of reforestation. The key findings are: (1) both deforestation and reforestation led to significant reductions in dry season runoff, while climate variability yielded positive effects in the studied watersheds; (2) the hydrological response to forest change varied over time due to changes in soil infiltration and evapotranspiration after vegetation regeneration; (3) changes of subalpine natural forests produced greater impact on dry season runoff than alteration of planted forests. These findings are beneficial to water resource and forest management under climate change and highlight a better planning of forest operations and management incorporated trade-off between carbon and water in different forests.

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In forest landscape restoration, one of the key objectives is to improve the water conservation capacity of the deforested land. A rapid, accurate assessment of the effects of the restoration measures on the water conservation capacity of targeted forests can help forest managers to identify the best practices for forest restoration. However, the traditional assessment tools of forest water conservation function lack a description of forest growth, and are featured by complex computation, which fails to evaluate the effects of forest restoration on the regional forest water conservation capacity in an efficient way. To address this issue, through combining the forest restoration evaluation model (equivalent recovery area, ERA), classic forest water storage capacity estimation (total water storage capacity), this study has taken advantage of ENVI/IDL, ArcGIS Engine/C#.Net to develop the Forest and Water Assessment Tool (FWAT) for assessing the changes of the regional forest landscape and the associated forest water conservation capacity in various forest restoration scenarios. This tool has been successfully applied in the Upper Zagunao watershed, a large forested watershed in the Upper Yangtze River basin. According to the assessment, the forest water conservation capacity of the study watershed consistently increased from about 1580.76 t/hm2 in 2010 to a projected 2014.34 t/hm2 by natural restoration, and 2124.18 t/hm2 by artificial restoration by 2030. The artificial restoration measures yield a better effect on forest water conservation function than natural restoration. By 2030, the forest water conservation capacity of artificial restoration scenario is expected to be about 7% higher than that of natural restoration scenario. The FWAT as an efficient tool to assess the effects of forest restoration measures on regional forest water conservation capacity can provide scientific support for the design of forest restoration and management strategies worldwide.

Abstract-Water conservation is one of the most important functions of forest ecosystems. An efficient assessment on changes in water conservation capacity of a forest watershed, especially for a large watershed is essential for water resources and forest management. In order to simplify the assessment procedures, we took advantage of ENVI / IDL and ArcGIS Engine / C # .NET hybrid programming languages and developed an assessment software (Forest Water Assessment Tool, FWAT) for calculating forest water conservation capacity based on the integrated water storage capacity method. In addition, we used the Meijiang watershed as an example to demonstrate the application of FWAT to calculate water conservation capacity. The spatial distribution and statistical results of forest water conservation capacity in the Meijiang watershed were successfully calculated by FWAT. It shows that FWAT is a very useful tool that can be widely used in evaluating water conservation capacity of forested watersheds and support decision-makers with a quick access to scientific information regarding forest and water management.