Abstract
Abstract There have been many studies on rainfall erosivity and erosivity density (ED). However, it was not widely developed in Indonesia as a tropical country and has unique precipitation patterns. They are indicators for assessing the potential risk of soil erosion. The Air Bengkulu Watershed is undergoing severe land degradation due to soil erosion. This study aimed to analyze spatial-temporal in rainfall erosivity and ED based on monthly rainfall data (mm). The data used consisted of 19 weather stations during the period 2006–2020 and which are sparsely distributed over the watershed. The analysis was done by using Arnold's equation. Then, the trend was tested using parametric and non-parametric statistics, and analysed with linear regression equation, and Spearman's Rho and Mann Kendall's tests. The spatial distribution of both algorithms was analysed using the inverse distance weighted (IDW) method based on the geographic information system (GIS). Unlike previous research findings, The long-term average monthly rainfall erosivity and ED revealed a general increase and decreasing trend, whereas it was found to be non-significant when both indices were observed. However, these results indicate a range from 840.94 MJ · mm−1 · ha−1 · h−1 · a−1, 552.42 MJ · mm−1 · ha−1 · h−1 · a−1 to 472.09 MJ · mm−1 · ha−1 · h−1 · a−1 in that November month followed by December and April are the most susceptible months for soil erosion. Therefore, The upstream area of the region shows that various anthropogenic activities must be managed properly by taking into account the rainfall erosivity on the environment and that more stringent measures should be followed in soil and water conservation activities.
Highlights
In most areas of the world, the current watershed conditions are deteriorating
The monthly period of maximum rainfall erosivity occurs in November, which is the highest peak of rainfall
The results show that rainfall erosivity is a relationship between rainfall erosivity and the conditions of monthly rainfall in the Air Bengkulu watershed (Table 3)
Summary
In most areas of the world, the current watershed conditions are deteriorating. Population density around it grows faces an excellent weight, as does the extensive use or exploitation of natural resources causing the watershed’s condition to deteriorate. Based on data from the Center for Watershed Management and Protected Forests (WMPF) Ketahun revealed damage to the watershed with an area of 626,000 ha of critical land and 99,000 ha of very critical land (Satmaidi et al 2018) This impacts the ability of watersheds to store water and increases the volume of water resulting in floods and landslides every year (Mase 2020). High rainfall at the study site causes soil erosion with surface runoff which triggers flood disasters (Ma et al 2020) and decreases water quality (Mahmud et al 2019). This is due to the conversion of forest areas for mining and plantation activities upstream of the Air Bengkulu watershed (Gunawan et al 2020)
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