Peri-Urban Amplification of Drought Stress

This interactive dashboard examines how rapid urbanization in Kathmandu Valley interacts with monsoon drought to amplify ecological stress in peri-urban grasslands. Analyzing 23 years (2000-2022) of MODIS LST/NDVI, ERA5-Land soil moisture, and TerraClimate ET₀ data, we identify a persistent peri-urban heat penalty (+0.94°C), elevated evaporative demand (+23.6 mm), and amplified vegetation stress (~4% greater NDVI decline) during droughts. These findings reveal that peri-urban ecosystems ;occupying the critical transition between urban heat islands and rural cool refuges ;face compound climate-urbanization risks that require targeted land management and thermal mitigation strategies.

Monsoon-season (June-October) Land Surface Temperature (LST) trends from 2000-2022 across urban, peri-urban, and rural grasslands in Kathmandu Valley. All zones show significant warming trends (p<0.01), with urban areas warming fastest (+0.107°C/year). Drought years (shaded, SPI < -0.75) correspond to LST spikes, particularly pronounced in peri-urban areas. The peri-urban zone maintains a persistent +~~1.01°C heat penalty relative to rural areas, demonstrating baseline urban heat island effects that amplify during climate extremes.

Normalized Difference Vegetation Index (NDVI) trajectories reveal differential vegetation stress responses across the urban-rural gradient. All zones exhibit declining trends (p<0.001), with urban areas showing the steepest degradation (-0.0066/year). During drought years, peri-urban grasslands experience ~4% greater NDVI decline compared to rural areas, despite partial thermal convergence. This amplified vegetation stress in peri-urban zones reflects compounded impacts of baseline warming and elevated evaporative demand, even when meteorological drought conditions are similar.

Reference evapotranspiration (ET₀) patterns show a consistent +23.6 mm average difference between peri-urban and rural grasslands, with peri-urban ET₀ elevated by 2.66% during drought episodes. Unlike LST and NDVI, ET₀ shows no significant temporal trends (p>0.05), indicating that atmospheric demand dominates over temporal variability. The persistent ET₀ gap reflects peri-urban microclimatic conditions (higher temperatures) that increase water demand and contribute to vegetation stress independent of precipitation deficits.

Non-parametric statistical analysis validates observed patterns using Mann-Kendall trend tests (α=0.05) and Mann-Whitney U tests comparing peri-urban versus rural zones. LST, NDVI, and ET₀ all show statistically significant differences between peri-urban and rural areas (p<0.05), confirming that urbanization creates distinct microclimatic and ecological regimes. Notably, soil moisture shows no significant difference (p=0.23), justifying its exclusion from primary analysis and indicating that peri-urban ecological stress is driven more by atmospheric demand (ET₀) and temperature than by soil water availability alone.

The peri-urban to rural LST gap quantifies the urban heat island intensity across the study period. The mean gap of +~~1.01°C (σ=0.77°C) exhibits high interannual variability, ranging from -1.22°C (2007) to +2.00°C (2021). This variability reflects the interaction between baseline urbanization effects and monsoon drought dynamics. During severe droughts, rural evaporative cooling collapses, causing thermal convergence (gap narrows to ~0.35°C). However, this convergence masks continued peri-urban vulnerability through elevated ET₀ demand and vegetation stress, demonstrating that thermal metrics alone underestimate ecological impacts in transitional landscapes.