A comparative performance analysis of three standardized climatic drought indices in the Chi River basin, Thailand

AbstractDrought indices are generally used as a tool for monitoring changes in drought conditions. This paper evaluated the performance of three climatic drought indices to characterize drought trends in the Chi River basin in Northeast Thailand. Initially, the drought assessment was conducted using the Standardized Precipitation Index (SPI), a precipitation-based index, and the Standardized Precipitation Evapotranspiration Index (SPEI), an index taking into account the difference between precipitation and potential evapotranspiration (PET). Then, this study simply applied an index called the Standardized Precipitation Actual Evapotranspiration Index (SPAEI), similar to the commonly used SPEI, with the difference being in the use of actual evapotranspiration (AET) instead of PET. Time series of the three indices were compared with observed droughts. The results indicated that various indicators of different indices can have diverse effects on drought conditions. The simple SPI, considering only precipitation, can be used to identify characteristics of droughts with certain restrictions. Being multivariate indices, the SPEI and the SPAEI were able to clearly detect the temporal variability of droughts to a greater extent than the SPI index. Moreover, the different results derived from using P-AET instead of P-PET made a substantial difference to temporal drought severity. Thus, climatic water demand had important aspects in determining the drought conditions for this area

Drought Characteristics in the Lower Mekong River Basin and Relationship to Land Cover Change

Drought can have devastating effects on regional water resources and agriculture, with an estimated US$96 billions of damages globally between 2005 and 2015. In the Lower Mekong Basin, the impacts of drought have been a major concern for local stakeholders as the region is the largest rice-producing area in the world. Few studies of long-term drought in the region have directly assessed the effects of land cover changes on both agricultural and hydrological drought. We used a suite of remote sensing data to assess drought characteristics in five countries of this region (Vietnam, Cambodia, Thailand, Laos, Myanmar) where traditional in-situ measurements are not generally available. In addition to satellite data, we used the Variable Infiltration Capacity (VIC) macroscale hydrologic model to simulate drought and evaluate its variability with land cover change. The simulations had a relatively high spatial resolution of 5 km, which facilitated the identification of local patterns of land cover change and their relationship with drought characteristics such as severity, duration, and onset. Our results confirmed that 25% of land cover has changed in the region over the last two decades (2001 to present) by using MODIS observation data. Furthermore, our simulations of drought from 1980 onwards, have allowed us to explore the link between land cover change and hydrological characteristics. and found that drought characteristics in the Mekong River basin do not appear to be significantly affected by land cover change

Indicator-to-impact links to help improve agricultural drought preparedness in Thailand

Droughts in Thailand are becoming more severe due to climate change. Developing a reliable Drought Monitoring and Early Warning System (DMEWS) is essential to strengthen a country&rsquo;s resilience to droughts. However, for a DMEWS to be valuable, the drought indicators it provides stakeholders must have relevance to tangible impacts on the ground. Here, we analyse drought indicator-to-impact relationships in Thailand, using a combination of correlation analysis and machine learning techniques (random forest). In the correlation analysis, we study the link between meteorological drought indicators and high-resolution remote sensing vegetation indices used as proxies for crop-yield and forest-growth impacts. Our analysis shows that this link varies depending on land use, season, and region. The random forest models built to estimate regional crop productivity allow a more in-depth analysis of the crop-/region-specific importance of different drought indicators. The results highlight seasonal patterns of drought vulnerability for individual crops, usually linked to their growing season, although the effects are somewhat attenuated in irrigated regions. Integration of the approaches provides new detailed knowledge of crop-/region-specific indicator-to-impact links, which can form the basis of targeted mitigation actions in an improved DMEWS in Thailand, and could be applied in other parts of Southeast Asia and beyond.</p

Implementing a new rubber plant functional type in the Community Land Model (CLM5) improves accuracy of carbon and water flux estimation

Rubber plantations are an economically viable land-use type that occupies large swathes of land in Southeast Asia that have undergone conversion from native forest to intensive plantation forestry. Such land-use change has a strong impact on carbon, energy, and water fluxes in ecosystems, and uncertainties exist in the modeling of future land-use change impacts on these fluxes due to the scarcity of measured data and poor representation of key biogeochemical processes. In this current modeling effort, we utilized the Community Land Model Version 5 (CLM5) to simulate a rubber plant functional type (PFT) by comparing the baseline parameter values of tropical evergreen PFT and tropical deciduous PFT with a newly developed rubber PFT (focused on the parameterization and modification of phenology and allocation processes) based on site-level observations of a rubber clone in Indonesia. We found that the baseline tropical evergreen and baseline tropical deciduous functions and parameterizations in CLM5 poorly simulate the leaf area index, carbon dynamics, and water fluxes of rubber plantations. The newly developed rubber PFT and parametrizations (CLM-rubber) showed that daylength could be used as a universal trigger for defoliation and refoliation of rubber plantations. CLM-rubber was able to predict seasonal patterns of latex yield reasonably well, despite highly variable tapping periods across Southeast Asia. Further, model comparisons indicated that CLM-rubber can simulate carbon and energy fluxes similar to the existing rubber model simulations available in the literature. Our modeling results indicate that CLM-rubber can be applied in Southeast Asia to examine variations in carbon and water fluxes for rubber plantations and assess how rubber-related land-use changes in the tropics feedback to climate through carbon and water cycling

Hydrometeorological Extremes and Its Local Impacts on Human-Environmental Systems

This Special Issue of Atmosphere focuses on hydrometeorological extremes and their local impacts on human–environment systems. Particularly, we accepted submissions on the topics of observational and model-based studies that could provide useful information for infrastructure design, decision making, and policy making to achieve our goals of enhancing the resilience of human–environment systems to climate change and increased variability

Underlying causes of Eurasian mid-continental aridity in simulations of mid-Holocene climate

The CMIP5/PMIP3 mid-Holocene simulations show drier conditions in the Eurasian mid-continent and a significant increase in summer temperature; in contrast, paleoenvironmental data (including lake level, vegetation and isotope records, and aeolian deposits) and quantitative climate reconstructions show that the mid-continental extratropics were wetter than today and summers were cooler (Harrison et al., 2015). Eurasian mid-continental aridity and warming has been a persistent feature of model simulations, already present in atmosphere-only simulations (Yu & Harrison, 1996) and appearing more strongly in coupled ocean-atmosphere simulations (e.g. Braconnot et al., 2007b; Wohlfahrt et al., 2008; Harrison et al., 2015) and further exacerbated by vegetation feedback (Wohlfarht et al., 2004). The consistency among multiple lines of paleoenvironmental evidence makes it unlikely that the mismatch reflects misinterpretation of the data. Regional temperature biases in the CMIP5 20th century simulations have been linked to biases in surface energy and water balances, with over- or under-prediction of moisture fluxes and evapotranspiration leading to cold and warm temperature biases respectively (Mueller & Seneviratne, 2014). This suggests that discrepancies in the simulation of mid-Holocene climates might have a similar cause. In this paper, we investigate the processes involved in mid-continental climate changes in the CMIP5/PMIP3 simulations in order to identify the underlying cause of the mismatch with observations

The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, similar to 6000 years before present). The main forcing that contributed to this intensification is related to changes in the Earth's orbital parameters. Nonetheless, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modeling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this re- mote influence is mediated by anomalies in Indian Ocean sea surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period

Impact of soil and water conservation measuren on catchment hydrological response: a case in north Ethiopia

Impact studies of catchment management in the developing world rarely include detailed hydrological components. Here, changes in the hydrological response of a 200-ha catchment in north Ethiopia are investigated. The management included various soil and water conservation measures such as the construction of dry masonry stone bunds and check dams, the abandonment of post-harvest grazing, and the establishment of woody vegetation. Measurements at the catchment outlet indicated a runoff depth of 5 mm or a runoff coefficient (RC) of 1·6% in the rainy season of 2006. Combined with runoff measurements at plot scale, this allowed calculating the runoff curve number (CN) for various land uses and land management techniques. The pre-implementation runoff depth was then predicted using the CN values and a ponding adjustment factor, representing the abstraction of runoff induced by the 242 check dams in gullies. Using the 2006 rainfall depths, the runoff depth for the 2000 land management situation was predicted to be 26·5mm(RCD 8%), in line with current RCs of nearby catchments. Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (ΔT) relative to the water surplus (WS) over the same period increased between 2002-2003 (ΔT/WS D 3·4) and 2006 (ΔT/WS >11·1). Emerging wells and irrigation are other indicators for improved water supply in the managed catchment. Cropped fields in the gullies indicate that farmers are less frightened for the destructive effects of flash floods. Due to increased soil water content, the crop growing period is prolonged. It can be concluded that this catchment management has resulted in a higher infiltration rate and a reduction of direct runoff volume by 81% which has had a positive influence on the catchment water balance. © 2010 John Wiley & Sons, Ltd

The Reliability of W-flow Run-off-Rainfall Model in Predicting Rainfall to the Discharge

This research intends to predict the discharge (run-off) from rainfall for which the model is built using W-flow. The research location is in the Gajah Mungkur reservoir (Wonogiri) in Indonesia. The estimation of reservoir inflow has an important role, mainly in the scheme of reservoir operation and management. However, the heterogeneity of complex spatial and temporal patterns of rainfall and also the physiographic context of a watershed cause the development of a model of real-time run-off and rainfall that can accurately predict the reservoir inflow to become a challenge in the development of water resources. In relation to the analysis and prediction of rainfall, the constraint and problem that is still often faced is the minimal availability of observed rainfall data spatially as well as temporally; the time series of rainfall data is not long and complete enough; and the number of rainfall stations is less evenly distributed. The methodology consists of carrying out the literature study, collecting as much rainfall data as possible to build a W flow model, then carrying out the model calibration and analyzing the prediction of real-time reservoir inflow for operation. The result shows that the dependable discharge of the Wonogiri watershed shows that there are two peak discharges, which happened on February II (the second half of February) and December II (the second half of December). However, the discharge is decreasing in July and reaching its lowest level in October II (the second half of October). Doi: 10.28991/CEJ-2023-09-07-015 Full Text: PD