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Sensitivity of forest mortality to drought in carbon-dense tropical forests remains fraught with uncertainty, while extreme droughts are predicted to be more frequent and intense. Here, the potential of temporal autocorrelation of high-frequency variability in Landsat Enhanced Vegetation Index (EVI), an indicator of ecosystem resilience, to predict spatial and temporal variations of forest biomass mortality is evaluated against in situ census observations for 64 site-year combinations in Costa Rican tropical dry forests during the 2015 ENSO drought. Temporal autocorrelation, within the optimal moving window of 24 months, demonstrated robust predictive power for in situ mortality (leave-one-out cross-validation R 2  = 0.54), which allows for estimates of annual biomass mortality patterns at 30 m resolution. Subsequent spatial analysis showed substantial fine-scale heterogeneity of forest mortality patterns, largely driven by drought intensity and ecosystem properties related to plant water use such as forest deciduousness and topography. Highly deciduous forest patches demonstrated much lower mortality sensitivity to drought stress than less deciduous forest patches after elevation was controlled. Our results highlight the potential of high-resolution remote sensing to "fingerprint" forest mortality and the significant role of ecosystem heterogeneity in forest biomass resistance to drought., (© 2021 John Wiley & Sons Ltd.)

Even though existing remote-sensing-based drought indices are widely used in many different types of ecosystems, their utility has not been widely assessed in tropical dry forests (TDFs). The aim of this study is to evaluate the performance of three remote-sensing-based drought indices, the Vegetation Condition Index (VCI), Temperature Condition Index (TCI), and Vegetation Health Index (VHI), for meteorological drought monitoring in TDFs using the moderate-resolution imaging spectroradiometer (MODIS) products. The correlation between the VCI, TCI, and VHI and multiple time scales of the Standardized Precipitation Index (SPI) (1, 3, 6, 9, 12, 15, 18, 21, 24 months) for each month (January to December) and each season (dry season, dry-to-wet season, wet season and wet-to-dry season) were conducted using the Pearson correlation analysis. We also correlated year-to-year changes of satellite-based drought indices with the changes of the in situ annual SPI (A_SPI) which provides annual information on the mean meteorological drought. The analysis reveals that the ability of these remote-sensing-based drought indices for meteorological drought monitoring varies with timing, and the TCI outperforms the VCI and VHI in terms of seasonal and annual scale. These remote-sensing indices performed well in monitoring meteorological drought in the dry season, poorly in the in the dry-to-wet season, and moderately in the wet season. The TCI performed best in monitoring meteorological drought in the wet-to-dry period, followed by VHI, whereas the VCI performed worst. All of these remote-sensing-based drought indices failed to detect drought in May during the green-up period and in September, October, and November when the water content in the root regions was abundant. Our results indicate that the evapotranspiration of TDFs is more sensitive than canopy greenness to detect meteorological drought. Results from this study increase the ability to provide real-time drought monitoring and early warnings of drought in TDFs.

Water scarcity and the difference between water supply and consumption is an increasing concern particularly under climatic uncertainty. Costa Rica has historically been at the forefront of environmental legislation; however, the water use framework in Costa Rica, still utilizes a quota style water allocation, which is problematic in extreme drought conditions. This allocation system paired with climate volatility makes it essential to quantify the future water demands compared to the water supply in Costa Rica. We use the Integrated Valuation of Ecosystem Services and Tradeoffs modeling system to quantify the water availability and usage in watersheds in Costa Rica under different climate and land cover change scenarios. We subsequently assess the spatial variability of water shortage and stress across Costa Rica. We find that there is a high spatial difference in water availability which do not match high use basins. In the highest demand areas, over 70 % of the water supply is projected to be consumed under a business-as-usual land cover change and high emission climate scenario. Low emission climate scenarios result in higher water availability, and increased forest regrowth increases water availability. Overall, the Guanacaste Province and the central valley which includes the capital city of San Jose are most at risk for experiencing high or moderate water shortage and stress in the future. Given the risks associated with water shortage and scarcity, it is important to address governance and stakeholder concerns as we move into the future. • There is a mismatch between areas of Costa Rican water supply and water demand. • Water stress and shortage are highest near the capital city of San Jose and on the Pacific side of Costa Rica. • Water usage highly related to urban and agricultural presence in the watershed. • Incentive structures could improve crop and water matching to reduce water stress. • Drought and flood management strategies should be implemented at a regional level. [ABSTRACT FROM AUTHOR]

Due to excessive human disturbances, as well as predicted changes in precipitation regimes, tropical dry forests (TDFs) are susceptible to meteorological droughts. Here, we explored the response of TDFs to meteorological drought by conducting temporal correlations between the MODIS-derived normalized difference vegetation index (NDVI) and land surface temperature (LST) to a standardized precipitation index (SPI) between March 2000 and March 2017 at the Santa Rosa National Park Environmental Monitoring Super Site (SRNP-EMSS), Guanacaste, Costa Rica. We conducted this study using monthly and seasonal scales. Our results indicate that the NDVI and LST are largely influenced by seasonality, as well as the magnitude, duration, and timing of precipitation. We find that greenness and evapotranspiration are highly sensitive to precipitation when TDFs suffer from long-term water deficiency, and they tend to be slightly resistant to meteorological drought in the wet season. Greenness is more resistant to short-term rainfall deficiency than evapotranspiration, but greenness is more sensitive to precipitation after a period of rainfall deficiency. Precipitation can still strongly influence evapotranspiration on the canopy surface, but greenness is not controlled by the rainfall, but rather phenological characteristics when leaves begin to senesce. [ABSTRACT FROM AUTHOR]

• The temporal response of TDFs to SST anomalies are assessed. • The impacts of El Niño events on TDFs are assessed by MWCA. • Teleconnection, biophysical characteristics, and seasonality influence the response of TDFs on ENSO. Tropical Dry Forests (TDFs) in the Americas are significantly affected by drought related to El Niño Southern Oscillation (ENSO). The analysis builds upon two drought indices: the MODIS-derived Vegetation Condition Index (VCI) and Temperature Condition Index (TCI) and the Sea Surface Temperature (SST) anomaly in the Niño 3.4 region. Temporal correlation analysis and Moving Window Correlation Analysis (MWCA) were used to explore the long-term and short-term responses at multiple sites. Results illustrate Gross Primary Productivity (GPP) at SRNP-EMSS (Santa Rosa National Park Environmental Monitoring Super Site) and PEMS (Parque Estadual da Mata Seca) in the dry season were negatively impacted by the long-term SST anomaly across multiple ENSO phases (warm, neutral, and cold phases), while there was no long-term impact at CCBR (Chamela-Cuixmala Biosphere Reserve) and TVMWR (Tucabaca Valley Municipal Wildlife Reserve). Findings from a short-term perspective, suggest that the GPP at SRNP-EMSS and CCBR were sensitive to the ENSO warm phase. TDFs GPP at PEMS and TVMWR were resistant to El Niño. Our results reveal that stronger El Niño events may lead to severe droughts in more regions across TDFs, but there is no direct relationship between the intensity of an individual El Niño event and the precipitation condition in each study site. Except for their teleconnections, the biophysical characteristics and seasonality can impact the response of ENSO on the GPP. [ABSTRACT FROM AUTHOR]