Mechanism and Refined Assessment of Valley Topography Effects on Solar Shortwave Radiation in the Grand Canyon: An XGBoost-SHAP-Based Analysis

Abstract

Accurate photovoltaic (PV) resource assessment relies on a clear understanding of how valley topography modulates incoming solar shortwave radiation, a process for which prior investigations have not fully established quantitative attribution of individual topographic driving factors. This study selects the Grand Canyon as the study area, and establishes a solar radiation estimation model based on the Extreme Gradient Boosting (XGBoost) algorithm, supported by hourly radiation data from the National Solar Radiation Database (NSRDB) and 30 m-resolution terrain data from the NASA digital elevation model (NASADEM) dataset. Residual analysis is applied to isolate the interference of temporal effects. SHapley Additive exPlanations (SHAP) framework is adopted to quantify the independent contributions. Model results reveal that aspect acts as the dominant topographic factor, while slope exerts the weakest influence. Topographic effects on radiation exhibit distinct diurnal variations: east-west slope differences are most prominent in the morning and north-south differences peak in the afternoon. These patterns remain consistent across all seasons. This study elucidates the modulation mechanism of valley topography on solar radiation, provides a methodological reference for refined solar resource assessment and PV site selection in regions with complex terrain.