This study compares copula regression, recently introduced in the forest biometric literature, with four benchmark regression models for computing wood volume V in forest stands given the values of diameter at breast height D and total height H, and suggests a set of statistical techniques for the accurate assessment of model performance. Two regression models deduced from the trivariate copulabased distribution of V, D, and H are tested against the classical Spurr's model and Schumacher-Hall's model based on allometric and geometric concepts, and two regression Keywords Fagus sylvatica Á Weighted regression Á Box-Cox transformation Á Copula regression Á Normal quantile transformation Á Uncertainty Communicated by G. Kändler.
The aim of this study is to assess the effectiveness of water trading policy as a solution for optimal use of water between farmers in Voshmgir dam, Iran. For assessment, four villages were selected and two water allocation programs under non-trading and trading systems were designed by two-stage stochastic programming technique and uncertainties expressed as intervals and probability distributions. The results obtained from the two programs were compared based on water volume which is released through trading and decrease in water deficiency as effectiveness indices. The results show that the water allocation under trading policy has changed so that it has led to released water and decrease in water deficiency by keeping the agricultural profit under non-trading, but irrigated area is decreased under trading. Generally, trading policy can lead to more effective allocation from the view of released water and decrease in water deficiency, but it can remove some farmers from agricultural activities by decreasing the irrigated area. As a result, trading policy can be effective in the short term especially in drought conditions due to insufficient water supply and can be unnecessary in normal and wet years in this case study.
Rangelands in the arid and semi-arid regions of Iran are under pressure from frequent degradations and extreme climate conditions, which have affected water conservation and delivery of ecosystem services. The timely and efficient assessment of rangeland state/condition impact on water conservation is crucial in rangeland management. This work represents an integrated modelling approach by linking the Soil and Water Assessment Tool (SWAT) and the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) models. SWAT simulated hydrologic components, while InVEST provided a decision support system for water conservation. The coupled SWAT-InVEST model was used to analyze the impact of different rangeland conditions on water conservation in the Atrak River basin in Iran's arid and semi-arid climatic zones. Increasing runoff is proportional to rangeland degradation. Our analysesshow a severe degradation of rangelands in Iran. We found that the basin's average runoff varies between 2 and 294.8 m 3 ha -1 yr -1 . Based on our modelling results, about 50% of the basin's runoff came from poor rangelands, 22% from moderate rangelands, and 28% from good rangelands. Thus, a significant impact on water conservation could be achieved through rangeland management in this basin. The SWAT-InVEST integrated modelling approach developed here proved useful for better decision-making under uncertainty.
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