Modeling seasonal rainfall erosivity on a regional scale: a case study from northeastern Iran

There is a need to analyze and map rainfall erosivity to assess soil erosion at the regional scale. The objectives of this study were to develop a regional model to estimate seasonal erosivity from seasonal rainfall data and to study temporal and spatial distribution of rainfall erosivity for the Gorganrood drainage basin in the northeast of Iran. Six gauging stations with a high temporal resolution [15 min] and eleven monthly totals stations located into the study area have been used. Regression models for pluviograph stations indicated that storm rainfall explained 22-51% of the variation in storm erosivity. But, at the seasonal scale, the explained variation increased to 62-86% and modified coefficient of efficiency increased from 0.12-0.29 to 0.38-0.64. Also, the results of ANOVA showed that EI[30] values have significant difference between autumn/ summer seasons and winter/spring seasons. Interpolation surfaces were created from all 17 stations seasonal values using the local polynomial algorithm. The results showed, during the wet season, erosivity varied from 438 Mj/mm/h [west] to 1015 Mj/ mm/h [Middle]. But, in the dry season, values of erosivity wrere lower than from values in wet season and the highest values were at the middle parts of the study area and the lowest were at the eastern and the western parts of the study area. Our findings provide good guidance to integrate pluviograph and pluviometric data for rainfall erosivity assessment in regional scales, where short duration rainfall intensity data, usually are not available

Flood occurrence hazard forecasting based on geographical information system

The application of Geographical Information system [GIS] in modeling flood and its prediction in catchments offers considerable potential. Several examples illustrate simple GIS techniques to produce flood hazard indices or its zonation using hydrologic-type models. Existing flood models can also be loosely coupled to a GIS, such as the HMS [Hydrological Modeling System] model. Forethermore, models can be fully integrated into a GIS by embedded coupling, such as the SCS [Soil Conservation Service] model. Installation of flood forecasting systems in watersheds with incomplete hydrometric data may reduce the flood-induced damages. In this study Geographical Information system used to up to date the watershed data and estimation of SCS model parameters which is sensible to considered the real time flood forecasting in Kasilian catchment of Mazandaran province. The main aim of this paper is to investigate the possibility of the linkage between GIS with a comprehensive hydrologic model, especially HMS. The use of GIS could produce a suitable agreement between observed results [extracted rainfall and runoff data of 1992, 1995 and 1996 from the related stations] with the calculated results of the hydrological model. The obtained results from rainfall-runoff process simulations of the model in this research showed that submergibility of the main watershed, Kasillian, does not depend on the outlet discharge rate of each one of its watershed independently. But it is related to how those two outlet hydrographs from main river watershed are combined. The model is capable of showing the flood characteristics temporally and spatially in each cross section of the channel network