Perbandingan Akurasi Model RUSLE dan WEPP untuk Prediksi Erosi pada Berbagai Penggunaan Lahan di Sub-DAS Bompon, Magelang

Muhammad Hafiz Syah, Nur Ainun Harlin Jennie Pulungan, S.Si., M.Sc., Ph.D. ; Dr. Agr. Makruf Nurudin, S.P., M.P. ; Tantriani, S,P., M.Agr. Ph.D.

2026 | Tesis | S2 Ilmu Tanah

Degradasi lahan akibat erosi tanah merupakan permasalahan ekologis yang mengancam keberlanjutan produktivitas pertanian di kawasan hulu daerah aliran sungai (DAS) tropis di Indonesia. Sub DAS Bompon, bagian dari DAS Bogowonto, dicirikan oleh topografi perbukitan vulkanik yang curam serta tanah dengan dominasi fraksi debu dan pasir sangat halus yang mudah tererosi, disertai kandungan lempung dengan kemantapan agregat rendah sehingga meningkatkan kerentanan terhadap erosi. Penelitian ini bertujuan mengestimasi laju erosi, mengklasifikasikan tingkat bahaya erosi, serta mengevaluasi kinerja komparatif model Revised Universal Soil Loss Equation (RUSLE) dan Water Erosion Prediction Project (WEPP). Data diperoleh melalui survei lapangan pada 36 titik pengamatan yang mewakili 12 satuan pemetaan lahan (SPL), dilengkapi analisis laboratorium terhadap tekstur tanah, berat volume, bahan organik, dan kapasitas tukar kation. Kinerja kedua model divalidasi menggunakan indikator erosi visual lapangan menurut Morgan (2005). Model RUSLE menghasilkan overall accuracy sebesar 72,22?ngan nilai Cohen's Kappa 0,65 (substantial agreement), namun cenderung mengestimasi tingkat bahaya erosi lebih tinggi pada lahan tegalan dan kebun campuran di lereng curam. Model WEPP mengestimasi laju erosi sebesar 4,28–337,55 ton ha?¹ tahun?¹, dengan lahan tegalan mencatat kehilangan tanah rata-rata tertinggi sebesar 139,73 ton ha?¹ tahun?¹. Secara keseluruhan, model WEPP memberikan prediksi yang lebih representatif terhadap kondisi aktual lapangan dibandingkan RUSLE. Hasil penelitian menunjukkan bahwa interaksi antara karakteristik tanah yang rentan terhadap erosi, pengelolaan lahan kering intensif, dan morfologi lereng yang curam merupakan faktor utama penyebab bahaya erosi di Sub DAS Bompon. Oleh karena itu, konservasi tanah secara terpadu melalui pendekatan mekanis dan agronomis perlu diprioritaskan, khususnya pada lahan tegalan di kawasan perbukitan.

Land degradation caused by soil erosion is a critical ecological issue threatening the sustainability of agricultural productivity in the upper reaches of tropical watersheds in Indonesia. The Bompon Sub-watershed, a tributary of the Bogowonto Watershed, is characterized by steep volcanic hills and erosion-prone soils dominated by silt, very fine sand, and clay with low aggregate stability. Erosion risk is further intensified by intensive dryland cultivation without adequate conservation practices. This study aimed to estimate soil erosion rates, classify erosion hazard levels, and evaluate the comparative performance of the Revised Universal Soil Loss Equation (RUSLE) and the physically based Water Erosion Prediction Project (WEPP) models. Field data were collected from 36 observation points representing 12 land mapping units (LMUs), complemented by laboratory analyses of soil texture, bulk density, organic matter content, and cation exchange capacity. Model performance was validated using field-based visual erosion indicators following Morgan (2005). The RUSLE model achieved an overall accuracy of 72.22% with a Cohen's Kappa coefficient of 0.65, indicating substantial agreement, but tended to overestimate erosion hazard on steep dryland agricultural and mixed garden areas. The WEPP model estimated annual soil loss ranging from 4.28 to 337.55 t ha?¹ yr?¹, with dryland agricultural land exhibiting the highest average soil loss (139.73 t ha?¹ yr?¹). Overall, WEPP produced predictions that more closely matched field conditions than RUSLE. These findings indicate that the combined effects of erosion-prone soils, intensive dryland cultivation, and steep slopes are the primary drivers of soil erosion in the Bompon Sub-watershed, highlighting the need for integrated mechanical and agronomic soil conservation practices.

Kata Kunci : Erosi tanah, RUSLE, WEPP, Sub DAS Bompon, Konservasi Tanah