Hydroclimatic Characteristics Research Articles

A time-space varying distributed unit hydrograph (TS-DUH) for operational flash flood forecasting using publicly-available datasets

Although flash floods originate in upstream (headwater) catchments causing hazards locally, they often occur at short time scales and affect widely while relatively small size catchments respond to intense rainfall systems. Due to the heavy cost of computing and parameterization, high resolution spatially distributed hydrological models are not effectively deployed for global or large-scale flash flood forecasting. This research proposes a Time-Space varying Distributed Unit Hydrograph (TS-DUH) based on publicly-available data for efficient global scale flash flood forecasting. TS-DUH estimates the runoff travel time (and flow velocity) from each location to the catchment outlet based on topographic and hydroclimatic characteristics, while it delineates the runoff-drainage process by emphasizing the heterogeneous and dynamic runoff contribution corresponding to rainfall and soil moisture variations. The excess rainfall is estimated by two methods: the Soil Conservation Service’s (SCS) curve (CN-Runoff), and the widely used Global Flood Monitoring System (GFMS) which provides both long-term (2000-present) well-archived and real-time online global runoff (GFMS-Runoff) prediction based on a distributed hydrological model. TS-DUH is first validated based on 6,324 flash flood events from 281 small-to-medium-sized catchments broadly distributed across the CONUS, using “perfect” precipitation input (i.e., NLDAS-2 for this study). TS-DUH calibrated with GFMS-Runoff shows better performance than using CN-Runoff, with a probability of detection (POD) value of 0.9 for all the events and 71% of them having a KGE metric above 0.5. More importantly, with the real-time satellite rainfall-driven GFMS-Runoff, the long-term (2003–2020) TS-DUH simulation shows better performance than GFMS, indicating promising value in global flash flood prediction of the TS-DUH-integrated GFMS.

Assessment of hydrological model performance in Morocco in relation to model structure and catchment characteristics

Study region30 catchments in Morocco. Study focusWe assessed the KGE performance of eight monthly lumped hydrological models forced by ground-based rainfall observations. We then examined how the performance relates to model complexity and structure, applied exploratory correlation analysis to identify the catchment features (over 200 features were considered) most significantly related to model performance, and investigated how these models respond to three rainfall forcings (ERA5, CHIRPS, and PERSIANN-CDR). New hydrological insights for the regionThe findings indicate that no hydrological model outperformed (or underperformed) consistently across all the catchments and that model performance depends more on model structure and hydro-climatic characteristics, particularly those related to calibration and calibration-validation data difference, than on model complexity and non-hydro-climatic features. The linearity between rainfall and runoff was the primary feature influencing model performance. Additionally, besides the expected improvement of model performance when forced with richer rainfall and runoff calibration data in terms of wet and dry years, our results show that this holds true even if the calibration data is only relatively richer than the validation data and that dry periods are more beneficial to model performance than wet periods. Lastly, all the models responded similarly to the different rainfall inputs; each model performed better when using ERA5 than when using CHIRPS and underperformed when using PERSIANN-CDR. The metric that best explained this similarity was the Pearson correlation coefficient between the precipitation products and observed runoff.

Hydroclimatic drivers of at‐a‐station hydraulic geometry of Brazilian rivers

The geometry of river channels defines their discharge conveyance capacity and can alter the flood regime. While most rivers follow the Theory of Hydraulic Geometry at-a-station power laws, the spatial patterns of exponents, coefficients, and hydrological controls beyond the scale of river reaches remain unclear. Here, we analyze 290 Brazilian river cross-sections to test the hypothesis that the hydraulic geometry is related to basin hydroclimatic characteristics, with a significant difference between humid and dry basins. We classify the basins draining to each cross-section according to the aridity index and the baseflow index, and analyze the controls on the exponents and coefficients (i.e., parameters) of the at-a-station hydraulic geometry power-laws. Our results show that the exponents and coefficients follow a spatially coherent pattern. The exponent of the width of AGH power law is related to the aridity of the basin, being larger in drier basins with a low baseflow index. The width and velocity coefficients are strongly dependent on the basin area. Whereas the velocity coefficient decreases in large basins, the width coefficient increases in large basins, and the spatial distribution of width exponent is related to the bankfull cross-section shape. The combined analysis of hydraulic geometry and basin characteristics is a promising tool for discharge estimation in ungauged basins, flood management, and maintenance of natural rivers.

Toward Improved Simulations of Disruptive Reservoirs in Global Hydrological Modeling

AbstractAccurate simulation of reservoirs has been a challenge for global hydrological models due to highly discontinuous water management and uncertainties in reservoir shape representation. In addition, at a global scale, it is crucial to consider those reservoirs that disrupt the downstream flow regime. We augment the mesoscale Hydrological Model with a newly developed lake module (LM) that incorporates an existing reservoir regulation scheme with non‐consumptive demand predictions from random forest. We also evaluate the sensitivity of reservoir shape on streamflow and evaporation for three shape approximations of varying complexities. We tested the LM across 31 non‐consumptive reservoirs covering an extensive range of hydroclimatic characteristics and demonstrate the applicability by using freely available global reservoir information. Streamflow simulations with reservoirs and model calibration show a median Kling‐Gupta Efficiency improvement of +0.94 (calibration) and +0.77 (validation) when compared against model simulations without reservoirs and default parameter set. We find reservoir evaporation highly sensitive to reservoir shape with half‐pyramid approximation consistently resulting in best fit at reservoirs with surveyed bathymetry. In contrast, the linear approximation (rectangular prism) produced a median bias of +114% relative to half‐pyramid, for estimating evaporation, across all the reservoirs. Streamflow simulations were insensitive to the reservoir shape. Our analysis shows that 30% of the non‐consumptive hydropower reservoirs of the GRanD data set are non‐disruptive and can be excluded without loss to model realism. Further work is necessary for testing the regulation approach in reservoirs with consumptive water usage.

Toward interpretable LSTM-based modeling of hydrological systems

Abstract. Several studies have demonstrated the ability of long short-term memory (LSTM) machine-learning-based modeling to outperform traditional spatially lumped process-based modeling approaches for streamflow prediction. However, due mainly to the structural complexity of the LSTM network (which includes gating operations and sequential processing of the data), difficulties can arise when interpreting the internal processes and weights in the model. Here, we propose and test a modification of LSTM architecture that is calibrated in a manner that is analogous to a hydrological system. Our architecture, called “HydroLSTM”, simulates the sequential updating of the Markovian storage while the gating operation has access to historical information. Specifically, we modify how data are fed to the new representation to facilitate simultaneous access to past lagged inputs and consolidated information, which explicitly acknowledges the importance of trends and patterns in the data. We compare the performance of the HydroLSTM and LSTM architectures using data from 10 hydro-climatically varied catchments. We further examine how the new architecture exploits the information in lagged inputs, for 588 catchments across the USA. The HydroLSTM-based models require fewer cell states to obtain similar performance to their LSTM-based counterparts. Further, the weight patterns associated with lagged input variables are interpretable and consistent with regional hydroclimatic characteristics (snowmelt-dominated, recent rainfall-dominated, and historical rainfall-dominated). These findings illustrate how the hydrological interpretability of LSTM-based models can be enhanced by appropriate architectural modifications that are physically and conceptually consistent with our understanding of the system.

How much we know about precipitation climatology over Tianshan Mountains––the Central Asian water tower

Tianshan Mountains are the headwater regions for the central Asia rivers, providing water resources for ecological protection and economic development in semiarid regions. Due to scarce observations, the hydroclimatic characteristics of the Tianshan Mountains Precipitation (TMP) measured over highland (>1500 m) regions remain to be revealed. Here, we show the TMP belongs to a monsoon-like climate regime, with a distinct annual range and a high ratio of summer-to-yearly rainfall, and exhibits six abrupt changes, dividing the annual cycle into six precipitation sub-seasons. Over the past 60 years, the yearly TMP has significantly increased by 17.3%, with a dramatic increase in winter (135.7%). The TMP displays a significant 40-day climatological intra-seasonal oscillation (CISO) in summer. The TMP CISO’s wet phase results from the confrontation of the eastward propagating mid-tropospheric Balkhash Lake Low and the southward migrating Mongolian High. The sudden changes in the two climatological circulation systems trigger TMP’s changes, shaping the 40-day CISO. Emerging scientific issues are also discussed.

Comparative analysis of hydroclimatic characteristics on the territory of the Amur, Angara-Yenisei and drainage Torey basins (Eastern Transbaikalia)

A comparative analysis of hydroclimatic characteristics was carried out on the territory of the Amur, Angara-Yenisei and Torey closed drainage basins of Eastern Transbaikalia. According to monitoring weather stations, high rates of air temperature growth have been established for the territory of the mountain-taiga zone of the Angara-Yenisei basin, where the linear trend was 2.2, while for the arid steppe zone of the Torey endorheic basin – 1.8. The smallest linear trend of 1.5 was identified for the territory of the Amur Basin. In all studied basins, synchronous cyclicity of precipitation and water levels was revealed against the background of their average annual decrease.

Multivariate regression trees as an “explainable machine learning” approach to explore relationships between hydroclimatic characteristics and agricultural and hydrological drought severity: case of study Cesar River basin

Abstract. The typical drivers of drought events are lower than normal precipitation and/or higher than normal evaporation. The region's characteristics may enhance or alleviate the severity of these events. Evaluating the combined effect of the multiple factors influencing droughts requires innovative approaches. This study applies hydrological modelling and a machine learning tool to assess the relationship between hydroclimatic characteristics and the severity of agricultural and hydrological droughts. The Soil Water Assessment Tool (SWAT) is used for hydrological modelling. Model outputs, soil moisture and streamflow, are used to calculate two drought indices, namely the Soil Moisture Deficit Index and the Standardized Streamflow Index. Then, drought indices are utilised to identify the agricultural and hydrological drought events during the analysis period, and the index categories are employed to describe their severity. Finally, the multivariate regression tree technique is applied to assess the relationship between hydroclimatic characteristics and the severity of agricultural and hydrological droughts. Our research indicates that multiple parameters influence the severity of agricultural and hydrological droughts in the Cesar River basin. The upper part of the river valley is very susceptible to agricultural and hydrological drought. Precipitation shortfalls and high potential evapotranspiration drive severe agricultural drought, whereas limited precipitation influences severe hydrological drought. In the middle part of the river, inadequate rainfall partitioning and an unbalanced water cycle that favours water loss through evapotranspiration and limits percolation cause severe agricultural and hydrological drought conditions. Finally, droughts are moderate in the basin's southern part (Zapatosa marsh and the Serranía del Perijá foothills). Moderate sensitivity to agricultural and hydrological droughts is related to the capacity of the subbasins to retain water, which lowers evapotranspiration losses and promotes percolation. Results show that the presented methodology, combining hydrological modelling and a machine learning tool, provides valuable information about the interplay between the hydroclimatic factors that influence drought severity in the Cesar River basin.

Variation of natural characteristics of Tanjero Basin in Sulaymaniyah Governorate using GIS

Objective: The research aims to clarify the natural factors of the Tanjero River Basin. The Tanjero River Basin is located within the complex region in terms of topography in northeastern Iraq, eastern Iraqi Kurdistan region, and southwest of Sulaymaniyah Governorate. It is bordered on the eastern side by the Shahrazur Plain, the Sourin Mountains, and the Kweiza and Azmar Heights. On the western side, it is bordered by the Bernan mountain range, and on the northern side it is adjacent to the starting point of the Doula Rut Heights and Birah Mah Karun Mountain, and it is surrounded from the south by Darbandikhan Lake administratively. Methodology: The current research relied on the descriptive and analytical approach in describing the phenomenon and analyzing it spatially, and the systematic approach in revealing the geographical factors causing the variation in water volume in the Tanjero River Basin and diagnosing the factors affecting it positively or negatively. Results: By presenting the problem, reviewing the data, as well as linking it to the results, it becomes clear to us the clear influence of natural factors on the variation and diversity in the natural characteristics of the Tanjiro Basin in Sulaymaniyah Governorate, and this proves the validity of the study’s hypothesis. Conclusion: The results show that the hydro-climatic budget in the Tanjiro Valley Basin is represented by the Khanaqin and Sulaymaniyah stations, which express the hydro-climatic characteristics in the Tanjiro Valley Basin, as the results of the water budget appear. According to table (1), the basin region is witnessing a water surplus because the effective amounts of rainfall exceed the amounts of evaporation and transpiration in the months “October, December, January, and February.” This surplus is within the Sulaymaniyah station, which represents the feeding area of the Tanjiro Basin. In the north, it was recorded the highest in January at (39.8) mm, while Khanaqin station witnesses a water deficit for all months and does not record any water surplus in its monthly characteristics, which represents the southern region of the basin’s extension range, and for this reason the water flow was described as the northern region in Sulaymaniyah is the recharge area and the southern area with a climate similar to Khanaqin station is the water drainage area of the basin.

Vegetation Greenness Sensitivity to Precipitation and Its Oceanic and Terrestrial Component in Selected Biomes and Ecoregions of the World

In this study, we conducted a global assessment of the sensitivity of vegetation greenness (VGS) to precipitation and to the estimated Lagrangian precipitation time series of oceanic (PLO) and terrestrial (PLT) origin. The study was carried out for terrestrial ecosystems consisting of 9 biomes and 139 ecoregions during the period of 2001–2018. This analysis aimed to diagnose the vegetative response of vegetation to the dominant component of precipitation, which is of particular interest considering the hydroclimatic characteristics of each ecoregion, climate variability, and changes in the origin of precipitation that may occur in the context of climate change. The enhanced vegetation index (EVI) was used as an indicator of vegetation greenness. Without consideration of semi-arid and arid regions and removing the role of temperature and radiation, the results show the maximum VGS to precipitation in boreal high-latitude ecoregions that belong to boreal forest/taiga: temperate grasslands, savannas, and shrublands. Few ecoregions, mainly in the Amazon basin, show a negative sensitivity. We also found that vegetation greenness is generally more sensitive to the component that contributes the least to precipitation and is less stable throughout the year. Therefore, most vegetation greenness in Europe is sensitive to changes in PLT and less to PLO. In contrast, the boreal forest/taiga in northeast Asia and North America is more sensitive to changes in PLO. Finally, in most South American and African ecoregions, where PLT is crucial, the vegetation is more sensitive to PLO, whereas the contrast occurs in the northern and eastern ecoregions of Australia.

Warming Air Temperature Impacts Snowfall Patterns and Increases Cold-Season Baseflow in the Liwiec River Basin (Poland) of the Central European Lowland

The rapidly changing climate affects vulnerable water resources, which makes it important to evaluate multi-year trends in hydroclimatic characteristics. In this study, the changes in cold-season temperature (November–April) were analyzed in the period of 1951–2021 to reveal their impacts on precipitation and streamflow components in the Liwiec River basin (Poland). The temperature threshold approach was applied to reconstruct the snowfall/rainfall patterns. The Wittenberg filter method was applied to the hydrograph separation. The Mann–Kendall test and Sen’s slope were applied to estimate the significance and magnitude of the trends. An assessment of the similarity between trends in temperature and hydroclimatic variables was conducted using the Spearman rank-order correlation. The shift-type changes in river regime were assessed via the Kruskal–Wallis test. The results revealed that temporal changes in both snowfall, rainfall, and baseflow metrics were significantly associated with increasing temperature. Over 71 years, the temperature rose by ~2.70 °C, the snowfall-to-precipitation ratio decreased by ~16%, the baseflow increased with a depth of ~17 mm, and the baseflow index rose by ~18%. The river regime shifted from the snow-dominated to the snow-affected type. Overall, this study provides evidence of a gradual temperature increase over the last seven decades that is affecting the precipitation phase and streamflow component partitioning in the middle-latitude region.

Climate change impact on hydro-climatic variables of Ribb watershed, Tana sub-basin, Ethiopia

In Ethiopia, the Ribb River is one of the tributaries of the Lake Tana sub-basin. Temperature, precipitation, and streamflow would all be affected by climate change in the Ribb watershed. As a result of the disruption of regular hydrological processes, these climate changes have an impact on water resources. The goal of this study was to look into the effects of climate change on the Ribb watershed’s hydro-climatic characteristics. The forecasted climatic data for rainfall and temperature (minimum and maximum) came from the CORDEX (Coordinated Regional Climate Downscaling Experiments) Africa database. Climate change consequences were investigated using RCP 4.5 emission scenarios for the 2021–2060 time range, compared to the 1985–2005 baselines. The observed precipitation and temperature data were used to adjust for bias. The simulation of stream flow was carried out using the semi-distributed and physically based soil and water assessment tool (SWAT). From 1997 to 2003, the model was calibrated, and from 2004 to 2007, it was validated. To determine the trend of the climate variables, trend test analyses were performed on the various time series data. In all of the experiments conducted, the trend test revealed that historical and forecast precipitation recording stations showed statistically negligible trends for all critical values. At a level of 0.05, the historical and prospective maximum and minimum temperature data revealed increasing patterns. In general, the results demonstrated that meteorological conditions cause the flow to decrease over the season. As a result, climate change will have an impact on the Ribb watersheds water resources.

Spatiotemporal hydroclimatic characteristics of arid and semi-arid river basin under climate change: a case study of Iraq

Spatiotemporal hydroclimatic characteristics of arid and semi-arid river basin under climate change: a case study of Iraq

Inconsistent Hydroclimate Responses in Different Parts of the Asian Monsoon Region during Heinrich Stadials

Abstract Heinrich (H) events are significant millennial climatic events that occurred during the last glacial period. Their footprints exited most parts of the global world, including the Asian monsoon (AM) region. However, the internal hydroclimatic characteristics of the AM system and their link to the external forcing during the H stadials are not fully understood. This study reconstructed monsoon precipitation changes during 33,000-12,500 a BP using grain size characteristics, elementary ratios, and pollen percentages from sediments of a crater lake (Tianchi Lake) in northeastern China. The H1 ~ H3 events are identified by high values of median grain size (MGS) and low values of Fe/Mn ratios and pollen percentages. By comparison with other records in the AM region, we found that H events in monsoon precipitation records were more obvious in the relatively higher-latitude region than in the lower-latitude sites. These inconsistent responses within the AM region during the H stadials might be attributed to both the high- and low-latitude climate processes.

A combined use of in situ and satellite-derived observations to characterize surface hydrology and its variability in the Congo River basin

Abstract. The Congo River basin (CRB) is the second largest river system in the world, but its hydroclimatic characteristics remain relatively poorly known. Here, we jointly analyse a large record of in situ and satellite-derived observations, including a long-term time series of surface water height (SWH) from radar altimetry (a total of 2311 virtual stations) and surface water extent (SWE) from a multi-satellite technique, to characterize the CRB surface hydrology and its variability. First, we show that SWH from altimetry multi-missions agrees well with in situ water stage at various locations, with the root mean square deviation varying from 10 cm (with Sentinel-3A) to 75 cm (with European Remote Sensing satellite-2). SWE variability from multi-satellite observations also shows a plausible behaviour over a ∼25-year period when evaluated against in situ observations from the subbasin to basin scale. Both datasets help to better characterize the large spatial and temporal variability in hydrological patterns across the basin, with SWH exhibiting an annual amplitude of more than 5 m in the northern subbasins, while the Congo River main stream and Cuvette Centrale tributaries vary in smaller proportions (1.5 to 4.5 m). Furthermore, SWH and SWE help illustrate the spatial distribution and different timings of the CRB annual flood dynamic and how each subbasin and tributary contribute to the hydrological regime at the outlet of the basin (the Brazzaville/Kinshasa station), including its peculiar bimodal pattern. Across the basin, we estimate the time lag and water travel time to reach the Brazzaville/Kinshasa station to range from 0–1 month in its vicinity in downstream parts of the basin and up to 3 months in remote areas and small tributaries. Northern subbasins and the central Congo region contribute highly to the large peak in December–January, while the southern part of the basin supplies water to both hydrological peaks, in particular to the moderate one in April–May. The results are supported using in situ observations at several locations in the basin. Our results contribute to a better characterization of the hydrological variability in the CRB and represent an unprecedented source of information for hydrological modelling and to study hydrological processes over the region.

Microbial Sulfate Reduction (MSR) as a Nature‐Based Solution (NBS) to Mine Drainage: Contrasting Spatiotemporal Conditions in Northern Europe

AbstractAn emerging solution in mine waste remediation is the use of biological processes, such as microbial sulfate reduction (MSR), to immobilize metals, reducing their bioavailability and buffering the pH of acid mine drainage. Apart from laboratory tests and local observations of natural MSR in, for example, single wetlands, little is known about spatiotemporal characteristics of freshwater MSR from multiple locations within entire hydrological catchments. We here applied an isotopic fractionation (δ34S values in SO42−) and a Monte Carlo‐based mixing analysis scheme to detect MSR and its variation across two major mining regions (Imetjoki, Sweden and Khibiny, Russia) in the Arctic part of Europe under different seasonal conditions. Results indicate a range of catchment‐scale MSR values in the Arctic of ∼5%–20% where the low end of the range was associated with the non‐vegetated, mountainous terrain of the Khibiny catchment, having low levels of dissolved organic carbon (DOC). The high end of the range was related to vegetated conditions provided by the Imetjoki catchment that also contains wetlands, lakes, and local aquifers. These prolong hydrological residence times and support MSR hot spots reaching values of ∼40%. The present results additionally show evidence of MSR persistence over different seasons, indicating large potential, even under relatively cold conditions, of using MSR as part of nature‐based solutions to mitigate adverse impacts of (acid) mine drainage. The results call for more detailed investigations regarding potential field‐scale correlations between MSR and individual landscape and hydroclimatic characteristics, which, for example, can be supported by the isotopic fractionation and mixing scheme utilized here.

Tree-Ring-Based Drought Reconstruction in Northern North China over the Past Century

A tree-ring width chronology was developed from the Chinese pine (Pinus tabuliformis) in northern North China. To acquire a long-term perspective on the history of droughts in this region, the Standardized Precipitation Evapotranspiration Index (SPEI) from August of the previous year to February of the current year was reconstructed for the period of 1903–2012 AD. The reconstruction explained 46.6% of the instrumental records over the calibration period of 1952–2012. Five dry periods (1916–1927, 1962–1973, 1978–1991, 1994–1999 and 2002–2005) and three wet periods (1908–1915, 1928–1961 and 1974–1977) were found in the reconstructed period, and most of the dry years (periods) in the reconstruction were supported by historical records. Comparisons between the reconstruction and other nearby dryness/wetness indices and precipitation reconstructions demonstrated a good repeatability and high reliability in our reconstruction. Spatial correlation implied that the reconstruction could represent regional hydroclimatic characteristics on a larger regional scale. Significant periodicities and correlations were observed between the reconstructed data and the quasi-biennial oscillation (QBO), El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), which suggested that the hydroclimatic variation in northern North China may be closely connected to remote oceans. The significant and high correlation between the reconstructed series and sea surface temperatures (SSTs) in the eastern equatorial and Southeast Pacific Ocean indicated that ENSO may be the main factor influencing the regional climate.

Asymmetry of Western U.S. River Basin Sensitivity to Seasonally Varying Climate Warming

AbstractFuture climate warming over the Western U.S. (WUS) is projected to be greater in summer than winter. Previous model‐based studies of large river basins in the WUS showed much different annual streamflow responses to warming in warm versus cool seasons. However, it remains unclear how the annual streamflow relative responses to seasonal warming (asymmetry) and drivers of the response asymmetry vary across the entire WUS at the catchment‐scale, and how the simulated results compare with observations. Here, we investigate the asymmetry of annual streamflow responses to warm versus cool season warming at the HUC‐8 level across the entire WUS using model simulations and observations. We also examine the asymmetries' relationship with land surface and hydroclimate characteristics, and the primary contributor to the response asymmetry for each HUC‐8 basin. The HUC‐8 level results reveal more complexity than do earlier analyses of much larger river basins. Over 25% of WUS area has annual streamflow increases in response to warming in at least one season (mostly cool season). Annual streamflow is most sensitive to warm season warming in cool, inland basins, especially the northern Columbia River basin and most of the Upper Colorado River Basin, and most sensitive to cool season warming in warm, coastal basins. This bi‐directional pattern is enhanced by vegetation coverage but weakened by long‐term snowpack decline. In coldest basins with short snow‐free seasons, net radiation changes dominate the streamflow response asymmetry. For basins with cold‐to‐intermediate temperatures, vapor pressure deficit changes dominate. For warmest basins, surface resistance changes dominate.

Hydro-climatic Characteristics of Yarlung Zangbo River Basin since the Last Glacial Maximum

Hydro-climatic Characteristics of Yarlung Zangbo River Basin since the Last Glacial Maximum

Impact of 2016 intense drought to small tropical reservoir: An early onset and late recovery experience in Timah Tasoh, Malaysia

This study investigates the hydrological drought impact during the extreme 2016 El-Nino to small tropical reservoir of Timah Tasoh, in Perlis, Malaysia. Small tropical reservoirs are important freshwater supplier due to its economic & strategic factors including (i) closer distance to inhabitants and agriculture footprints, (ii) easy access to the resource, and (iii) cheaper cost of water pipelines system. In theory, small tropical lakes or reservoirs are facing higher risk to drought compared to the bigger ones. However, detail information and evidence are required for site specific drought adaptation in the future especially the onset and offset of the drought at specific hydrometeorological and dam scale. Prior to that, a case study was conducted in one of the small-sized and shallow reservoirs of Timah Tasoh, Perlis to analyze the impact. The larger Pedu reservoir was selected as control site. Both reservoirs were having identical hydro-climatic characteristics (seasonality of rainfall). The observation on the rainfall and reservoir level data indicated that the small sized reservoir (Timah Tasoh) tends to dry about 2 months faster (reached dam critical level) and recover 1 month late compared to the normal dry season. In comparison with the Pedu reservoir, the drought onset and offset in Timah Tasoh was earlier and late respectively although the rainfall pattern is typical. The total impacted drying days for Timah Tasoh is 197 days compared to 78 days of Pedu (about 3 months longer). The findings indicate that the 2016 extreme drought impacted the Timah Tasoh small reservoir where they would suffer longer dry season and experienced slower recovery compared to the bigger Pedu reservoir. The outcome of this investigation signifies that the early drought onset monitoring should be implemented for the small sized reservoirs to take appropriate mitigation and preventive measures in adapting to the intense drought.