Hydrological Research Letters - Original Research Letter - Does intensification of human activity occur near rivers in reported drought event years?

Sep 17, 2026

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Drought is examined as a socio-environmental process shaped by natural climatic variability and social factors affecting human activity near available water resources. While drought impacts on migration and settlement patterns are well studied, the spatial link between human activity changes and reported drought-affected regions is unclear. This study tests whether human activity intensifies near rivers in drought event years using harmonized nighttime light as a proxy and Geocoded Disaster records from 2001–2020, finding more frequent positive deviations near rivers and implications for drought vulnerability and water-resource planning.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Introduction

Socio-environmental framing of drought

Prior studies and research gap

Study approach and data sources

Abstract

Research question and motivation

Methods and data

Key findings and implications

Hydrological Research Letters 20(3), 191–198 (2026) Published online in J-STAGE ([www.jstage.jst.go.jp/browse/hrl). DOI: 10.3178/hrl.26-00011](www.jstage.jst.go.jp/browse/hrl). DOI: 10.3178/hrl.26-00011)[ ](www.jstage.jst.go.jp/browse/hrl). DOI: 10.3178/hrl.26-00011)Original Research Letter Does intensification of human activity occur near rivers in reported drought event years? Muhammad Shiraz Riaz, Sneha Kulkarni and Yohei Sawada Department of Civil Engineering, The University of Tokyo, Japan Abstract: Although natural climatic variations often lead to drought, it is a complex phenomenon shaped by both envi‐ ronmental and social factors. In water-scarce regions, human activity near available water resources may influ‐ ence how drought impacts are experienced. While the effects of drought on migration and human settlement pat‐ terns have been widely studied, the spatial relationship between changes in human activity and reported droughtaffected regions remains less understood. Here, we investi‐ gate whether human activity intensification occurs near rivers during reported drought event years. We use harmo‐ nized global Nighttime Light (NTL) data as a proxy for human activity and settlement intensity and analyze its spa‐ tial relationship with drought events recorded in the Geocoded Disaster (GDIS) database from 2001 to 2020. For each drought event, we calculate NTL-weighted cen‐ troids based on harmonized NTL intensity and assess their distance to nearby river networks. Results show that posi‐ tively deviated NTL changes occur more frequently near rivers than negatively deviated NTL changes in reported drought event years. This suggests that river-proximal drought-affected areas may experience intensified human activity or settlement intensity, which is relevant for drought vulnerability and water-resource planning. These findings highlight the need to consider human activity pat‐ terns near rivers when assessing reported drought impacts. KEYWORDS nighttime light; drought vulnerability; human activity intensification; river proximity; settlement intensity; climate risk INTRODUCTION Drought remains one of the most critical global environ‐ mental challenges, causing food insecurity, human dis‐ placement, economic losses, and water-supply disruptions (Ceola et al., 2023; Meng et al., 2025) . Traditionally, drought studies have focused on climate-driven variables such as precipitation deficits and evapotranspiration rates (Vicente-Serrano et al., 2010) . However, recent studies have emphasized socio-environmental frameworks that integrate both natural and anthropogenic drivers, highlight‐ ing the need to understand how human activities and envi‐ Correspondence to: Muhammad Shiraz Riaz, Department of Civil Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. E-mail: [shirazriaz1@gmail.com](shirazriaz1@gmail.com) ronmental change interact to shape drought dynamics (Aghakouchak et al., 2014; Van Loon et al., 2016; Kulkarni and Sawada, 2025a) . Recent global trends show increasing human mobility and settlement changes driven by socio-political and envi‐ ronmental stresses (Black et al., 2011) . These changes may alter local exposure and pressure on resources, particularly water, in vulnerable regions. Although previous studies have recognized the role of migration and settlement dynamics in relation to water availability and human vul‐ nerability (Hugo, 2011), the spatial relationship between human activity changes and reported drought-affected areas remains less understood. Investigating this relationship could improve drought vulnerability assessment, especially where human activity is concentrated near water resources. Previous works have primarily examined drought as adriver of migration, with water scarcity and agricultural decline contributing to displacement. Ceola et al. (2023), for example, applied Nighttime Light (NTL) data (NOAA, 2020) to explore how human settlem

FAQs

What research question does the letter address?

It investigates whether human activity intensification occurs near rivers during years when drought events are reported.

How is human activity measured in the study?

Harmonized nighttime light (NTL) data are used as a proxy for human activity and settlement intensity.

What do the results suggest about drought-affected regions near rivers?

Positively deviated NTL changes occur more frequently near rivers than negatively deviated changes, indicating intensified human activity or settlement intensity in river-proximal drought-affected areas.

Sep 17, 2026

Uploaded by Xiajie