Tanzania's Compound Environmental Crisis of 2023-2025
El Niño-Induced Floods, Cyclone Hidaya, Landslide Catastrophe, and Concurrent Drought a Geospatial and Hydroclimatic Analysis
THE GEOGRAPHICAL EYE-Environmental Research $ GIS Division
Recieved:15 January 2025 Revised:12 April 2025 Accepted: 19 May 2026
ABSTRACT
This paper investigates Tanzania's compound environmental crisis of 2023–2025, which represents the most severe multi-hazard disaster sequence in the country's post-independence history. Driven by the convergence of an anomalously strong El Niño event and a record-positive Indian Ocean Dipole (IOD), the crisis unfolded in three analytically distinct but physically interconnected phases: (i) catastrophic debris flows from Mount Hanang in Manyara Region (December 2023), killing 89 people and affecting 44,000; (ii) sustained El Niño-induced flooding across 17 of Tanzania's 26 administrative regions (January–May 2024), culminating in Cyclone Hidaya the strongest tropical cyclone ever to make landfall in Tanzania on 4 May 2024; and (iii) a concurrent and ongoing drought emergency in the central and northern plateau, characterised by Standardised Precipitation Index (SPI-6) values below −1.8 and critically low water levels at the Bahi Swamp Ramsar site. Drawing on multi-source geospatial analysis (Sentinel-1 SAR, CHIRPS, MODIS, GRACE, SRTM, GPM IMERG), World Bank damage and loss assessment data, IFRC humanitarian records, and peer-reviewed climatological literature, this study quantifies the total damage at US$553.08 million and documents impacts across agriculture (105,463 ha inundated), infrastructure (1,904 road sections; 121 bridges), education (897 schools; 209,581 students affected), and energy (4.7 million people without power). The paper advances three analytical arguments: first, that the dual-hazard character of the crisis (simultaneous flood and drought) reflects a structural transformation in Tanzania's climate risk landscape under anthropogenic forcing; second, that deforestation at 400,000 ha yr⁻¹ is a critical non-climatic amplifier of both hazard pathways; and third, that existing disaster risk governance frameworks are structurally misaligned with the compound-hazard reality now confronting the country. The paper concludes with a GIS data framework and research-informed policy synthesis.
Key Words:
Tanzania; El Niño; Indian Ocean Dipole; Cyclone Hidaya; Mount Hanang; compound climate hazard; flood risk; drought; deforestation; GIS; disaster risk governance; East Africa
INTRODUCTION
East Africa is widely recognized as one of the world's most climate-vulnerable regions, characterized by high exposure to rainfall variability, drought, and flooding, and constrained adaptive capacity rooted in widespread rural poverty, natural resource dependence, and limited institutional preparedness (IPCC, 2021; Nicholson, 2000). Within this regional context, Tanzania occupies a position of particular analytical interest: its climate system spans the bimodal equatorial regime of the Great Lakes Zone, the unimodal semi-arid central plateau, and the Indian Ocean monsoon-influenced coast, generating a heterogeneous hazard landscape in which drought and flood risks co-exist across distinct ecological zones.
The period from November 2023 to mid-2025 saw this risk landscape translate into a compound environmental crisis of unprecedented scale. Beginning with a meteorological warning from the Tanzania Meteorological Authority (TMA) in August 2023 forecasting above-normal rainfall driven by the simultaneous development of a strong El Niño and an anomalously positive Indian Ocean Dipole the crisis escalated through catastrophic debris flows, sustained riverine flooding, the record-breaking landfall of Cyclone Hidaya, and a concurrent drought emergency in the central and northern regions. The Government of Tanzania declared a National State of Emergency on 26 May 2024 (GoT, 2024).
Despite the severity and novelty of this compound event sequence, no systematic peer-reviewed analysis has yet integrated its climatic drivers, geospatial footprint, environmental consequences, and structural root causes within a single analytical framework. This paper seeks to fill that gap. The research is guided by three principal questions:
– What atmospheric and
oceanographic conditions drove the extreme hydrometeorological events of
2023–2025, and how do they situate within the broader context of anthropogenic
climate change and East African climate variability?
– What were the
documented environmental, infrastructural, agricultural, and ecological impacts
of the crisis, and how can geospatial analysis advance impact quantification
and spatial risk characterization?
– What structural non-climatic factors particularly deforestation and disaster risk governance amplified the crisis, and what do these findings imply for Tanzania's climate adaptation and disaster risk reduction (DRR) policy architecture?
The paper is structured as follows. Section 2 outlines the data sources and analytical methodology. Section 3 describes the climatic and atmospheric drivers. Section 4 presents the crisis chronology and case study analysis, with particular attention to the Mount Hanang debris flows and Cyclone Hidaya. Section 5 quantifies environmental and socioeconomic impacts. Section 6 examines structural drivers. Section 7 presents the GIS data framework. Section 8 discusses the findings in relation to existing literature and policy. Section 9 concludes.
DATA SOURCES AND METHODOLOGY
Geospatial Data Sources
This study integrates multiple geospatial datasets to characterise the spatial extent, intensity, and environmental consequences of the 2023–2025 Tanzania crisis. Rainfall anomalies were assessed using the Climate Hazards Infrared Precipitation with Stations version 2.0 (CHIRPS; Funk et al., 2015), a quasi-global daily precipitation product spanning 1981 to present at 0.05° (~5 km) spatial resolution. Drought severity was quantified using the Standardised Precipitation Index (SPI) at 3- and 6-month accumulation windows (McKee et al., 1993), calculated from CHIRPS gridded fields across Tanzania's central and northern regions.
Flood inundation mapping was conducted using Sentinel-1 Synthetic Aperture Radar (SAR) Ground Range Detected (GRD) imagery in C-band (10 m resolution), obtained from the ESA Copernicus Open Access Hub. The dual-polarisation (VV+VH) SAR backscatter change detection methodology comparing pre-event (September 2023) and during-event (April–May 2024) image pairs was applied to delineate flood inundation extents across the Rufiji, Wami-Ruvu, and coastal plain systems. These outputs were supplemented with MODIS Near-Real-Time Flood Monitoring products from NASA LANCE/FIRMS at 250 m resolution for rapid temporal coverage.
Topographic analysis and landslide susceptibility assessment for the Mount Hanang case study utilised the NASA/USGS Shuttle Radar Topography Mission (SRTM) 30 m Digital Elevation Model (DEM), from which slope angle, aspect, and curvature rasters were derived in QGIS 3.34. Satellite imagery from Planet Labs Super Dove (3 m multispectral), captured on 21 December 2023, provided direct post-event evidence of debris flow scarp morphology on Mount Hanang's northwest flank (Petley, 2024). ERA5 reanalysis data from the Copernicus Climate Data Store (ECMWF) provided sea surface temperature (SST), mean sea-level pressure, and atmospheric circulation fields for driver analysis. Cyclone Hidaya's track, intensity, and wind radii were sourced from the IBTrACS (International Best Track Archive for Climate Stewardship) database (Knapp et al., 2010).
Groundwater storage anomalies across the central plateau were assessed using GRACE/GRACE-FO Terrestrial Water Storage (TWS) anomaly products from NASA JPL (Tapley et al., 2019). Vegetation condition and drought proxy analysis utilised MODIS NDVI (MOD13Q1) at 250 m resolution, with the Vegetation Condition Index (VCI) computed relative to the 2000–2022 baseline climatology. Land use and land cover data were sourced from ESA WorldCover 2021 (10 m) and the Hansen Global Forest Change dataset (University of Maryland/Google Earth Engine), which provides annual forest cover loss at 30 m resolution from 2000 to 2023 (Hansen et al., 2013).
Non-Geospatial Data Sources
Quantitative impact data were primarily sourced from the World Bank's Crisis Response Window Plus (CRW+) eligibility document (World Bank, 2024a), which contains the most comprehensive rapid damage and loss assessment available for the 2023–2024 event sequence, incorporating sector-level data collected as of 30 May 2024. Complementary humanitarian impact data were drawn from successive IFRC Emergency Appeal operation updates (MDRTZ035; IFRC, 2024a; 2024b; 2024c) and the Government of Tanzania Prime Minister's Office parliamentary statements (GoT/PMO, 2024a; 2024b). Food security conditions were contextualised using FEWS NET Integrated Phase Classification (IPC) data for Tanzania and the East African region.
Where official government impact statistics were inconsistent across sources a common issue in rapidly evolving multi-hazard events this study has adopted the most conservative (lowest) figure for mortality and the most comprehensive (highest) figure for affected area, clearly flagging discrepancies in the text. All monetary values are expressed in 2024 United States Dollars unless otherwise stated.
Analytical Framework
The analytical framework adopted in this study draws on two established conceptual lenses from the disaster risk and climate science literature. First, the compound event framework of Zscheischler et al. (2020) is applied to characterise the concurrent flood-drought dynamics observed in Tanzania's 2023–2025 crisis, recognising that events driven by multiple interacting atmospheric, hydrological, and land-surface processes generate impacts that are non-linearly greater than the sum of their parts. Second, the Pressure and Release (PAR) model of Blaikie et al. (1994) subsequently updated by Wisner et al. (2004) is used to situate the crisis within a structural vulnerability framework that foregrounds root causes (deforestation, governance failures) alongside the immediate triggers (extreme rainfall, cyclone landfall).
ATMOSPHERIC AND OCEANOGRAPHIC DRIVERS
The 2023–2024 El Niño event was among the strongest in the instrumental record, with the Niño-3.4 Sea Surface Temperature (SST) anomaly reaching +2.0°C by November 2023 and sustaining above +1.5°C through the following boreal spring. The concurrent development of a strongly positive Indian Ocean Dipole (IOD) characterised by warm SST anomalies exceeding +2.5 standard deviations in the western Indian Ocean basin created an atmospheric configuration of exceptional moisture convergence over East Africa (Black et al., 2003; Behera et al., 2005). ERA5 reanalysis fields confirm anomalous lower-tropospheric easterly flow along the East African coastline during October–December 2023, driving enhanced moisture transport from the warm western Indian Ocean into the Tanzanian interior.
The co-occurrence of strong El Niño and strongly positive IOD is a recognised precursor to extreme Short Rains (OND) season precipitation over equatorial East Africa (Hastenrath et al., 1993; Nicholson, 2000). However, the 2023–2024 event was unusual in its persistence: above-normal rainfall continued through the Masika long rains (MAM 2024) rather than returning to near-normal conditions as is typically observed in a post-El Niño transition. TMA operational analysis attributed this persistence to anomalously warm SSTs throughout the western Indian Ocean that were maintained by background anthropogenic warming superimposed on the natural ENSO cycle a configuration consistent with observed trends toward more intense and longer-duration IOD events under continued greenhouse forcing (Cai et al., 2014).
Cyclone Hidaya:Internsification and Landfall Dynamics
Cyclone Hidaya developed from a tropical depression in the southern Indian Ocean in late April 2024 and underwent rapid intensification before making landfall on Tanzania's Mafia Island Archipelago on 4 May 2024. IBTrACS data indicate that Hidaya achieved maximum sustained winds of approximately 120 km h⁻¹ (Category 1 equivalent on the Saffir-Simpson scale) at landfall, with a minimum central pressure of ~975 hPa. The storm system was the strongest tropical cyclone ever recorded to make landfall on the Tanzanian mainland, surpassing previous records in the instrumental record (TMA, 2024; Center for Disaster Philanthropy, 2024).
Cyclone Hidaya's intensity was sustained by SSTs exceeding 29°C in the western Indian Ocean approximately 1.2°C above the climatological May baseline consistent with the background Indian Ocean warming trend identified in satellite-era SST records (Roxy et al., 2014). The cyclone's rainfall footprint was extreme: the TMA recorded 316 mm of rainfall at Kilwa within 36 hours of Hidaya's landfall, a figure described by Prime Minister Majaliwa in parliamentary testimony as equivalent to three years' typical May rainfall for that location (GoT/PMO, 2024b). Regions along the southern coast received more than 140% of their average monthly rainfall during the storm period (TRCS/IFRC, 2024).
Concurrent Drought in the Central Plateau
While extreme rainfall dominated the coastal and highland regions, large areas of Tanzania's central plateau particularly Dodoma, Singida, and northern Manyara regions entered prolonged drought conditions during the 2024 Masika season. CHIRPS-derived SPI-6 anomalies for the April–September 2024 window fell below −1.8 across approximately 140,000 km² of the central plateau, placing these regions in the severe drought classification according to the WMO SPI interpretation guidelines (McKee et al., 1993). MODIS VCI analysis confirms that vegetation stress anomalies exceeded −2.5 standard deviations below the 2000–2022 mean in Dodoma and Singida districts during the same period, indicating severe agricultural drought stress.
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