A Near Four-Decade Time Series Shows the Hawaiian Islands Have Been Browning Since the 1980s

Abstract

The Hawaiian Islands have been identified as a global biodiversity hotspot. We examine the Normalized Difference Vegetation Index (NDVI) using Climate Data Records products (0.05 × 0.05°) to identify significant differences in NDVI between neutral El Niño-Southern Oscillation years (1984, 2019) and significant long-term changes over the entire time series (1982–2019) for the Hawaiian Islands and six land cover classes. Overall, there has been a significant decline in NDVI (i.e., browning) across the Hawaiian Islands from 1982 to 2019 with the islands of Lāna’i and Hawai’i experiencing the greatest decreases in NDVI (≥44%). All land cover classes significantly decreased in NDVI for most months, especially during the wet season month of March. Native vegetation cover across all islands also experienced significant declines in NDVI, with the leeward, southwestern side of the island of Hawai’i experiencing the greatest declines. The long-term trends in the annual total precipitation and annual mean Palmer Drought Severity Index (PDSI) for 1982–2019 on the Hawaiian Islands show significant concurrent declines. Primarily positive correlations between the native ecosystem NDVI and precipitation imply that significant decreases in precipitation may exacerbate the decrease in NDVI of native ecosystems. NDVI-PDSI correlations were primarily negative on the windward side of the islands and positive on the leeward sides, suggesting a higher sensitivity to drought for leeward native ecosystems. Multi-decadal time series and spatially explicit data for native landscapes provide natural resource managers with long-term trends and monthly changes associated with vegetation health and stability.

Climate-Induced Forest Mortality in the Tropical Pacific Islands: What Do We Really Know?

“…Widespread warming has had a subsequent impact on the availability of water. Frazier and Giambelluca (2017) showed that Hawaiian Islands became increasingly drier between 1920 and 2012, a trend that was already noted by Doty (1982) and has continued in the state (Madson et al 2023), particularly during ENSO events (Frazier et al 2022). A similar pattern was documented by McGree et al (2016) throughout the Pacific Islands and northeast Australia, where the frequency, magnitude, and duration of drought events were revealed to be increasing.…”

Cap. 30. Hawái y las Islas del Pacífico Afiliadas a los Estados Unidos. En: La Quinta Evaluación Nacional del Clima

“…En Hawái, las sequías pasadas y la variabilidad de las precipitaciones tuvieron impactos a nivel de paisaje en la vegetación 364,365 e impactos ecológicos en cascada 366 . Es probable que los cambios climáticos a largo plazo aceleren la contracción del área de distribución y las tasas de extinción 93,367 , pero las respuestas variarán según las especies, incluidas las diferencias de tolerancia a la sequía entre poblaciones 368,369,370,371 .…”

“…En cuanto a las plantas nativas, ya se ha demostrado que los cambios climáticos influyen en las comunidades de plantas, desde amplios cambios en el paisaje hasta tendencias poblacionales de especies individuales (muy probable, alta confianza) 364,365,366,370 . Las proyecciones futuras indican efectos continuos y drásticos 93,367 .…”

Mapping Small-Scale Willow Crops and Their Health Status Using Sentinel-2 Images in Complex Agricultural Areas

“…In particular, VIs have been developed to assess a wide range of environmental and biological events [20,21] and may be used to forecast plants' biophysical characteristics [22]. Climate change, land-use change, and natural disturbances such as wildfires and insect outbreaks can all have an impact on vegetation greening and browning patterns [23][24][25], while VIs estimated from the red and near-infrared (NIR) bands are still commonly used in this context [26]. The normalized difference vegetation index (NDVI) [27] is commonly used to quantify vegetation changes and to study the effects of environmental events.…”