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Drought is a prominent feature of Hawaiʻi’s climate. However, it has been over 30 years since the last comprehensive meteorological drought analysis, and recent drying trends have emphasized the need to better understand drought dynamics and multi-sector effects in Hawaiʻi. Here, we provide a comprehensive synthesis of past drought effects in Hawaiʻi that we integrate with geospatial analysis of drought characteristics using a newly developed 100-year (1920–2019) gridded Standardized Precipitation Index (SPI) dataset. The synthesis examines past droughts classified into five categories: Meteorological, agricultural, hydrological, ecological, and socioeconomic drought. Results show that drought duration and magnitude have increased significantly, consistent with trends found in other Pacific Islands. We found that most droughts were associated with El Niño events, and the two worst droughts of the past century were multi-year events occurring in 1998–2002 and 2007–2014. The former event was most severe on the islands of O’ahu and Kaua’i while the latter event was most severe on Hawaiʻi Island. Within islands, we found different spatial patterns depending on leeward versus windward contrasts. Droughts have resulted in over $80 million in agricultural relief since 1996 and have increased wildfire risk, especially during El Niño years. In addition to providing the historical context needed to better understand future drought projections and to develop effective policies and management strategies to protect natural, cultural, hydrological, and agricultural resources, this work provides a framework for conducting drought analyses in other tropical island systems, especially those with a complex topography and strong climatic gradients.

Climate change is impacting public health in the Republic of the Marshall Islands (RMI). Meanwhile, migration within the RMI and abroad is driven, in part, by access to better healthcare, and migration is also expected to be accelerated by climate change. Based on a survey of 199 RMI households, this study used logistic regression and hierarchical clustering to analyze the relationships between climate stressors, climate-related health impacts, and migration outcomes and identify vulnerable segments of the population. Climate stressors were experienced by all respondents but no significant correlations were found between stressors, health impacts, and expectation to migrate. When grouped according to the climate stressors they faced, however, one group was characterized by low stressors, high wealth, and a low expectation to migrate, whereas another experienced very high climate stressors, low wealth, and a high expectation to migrate. Only the first exhibited a statistically significant relationship between climate-related health impacts and migration; however, for the second, climate stressors were significantly related to proximate determinants of health, and there was no association with migration. To create equitable adaptation outcomes across diverse society, policies should expand economic and education prospects and reduce vulnerability to the direct and indirect health impacts of climate change. Graphical Abstract Households that were surveyed in the Marshall Islands have experienced many climate stressors and direct impacts to health, as well as the determinants of health, in recent years.

Groundwater sustainability initiatives, including sustainable yield and watershed policy protection policies, are growing globally in response to increasing demand for groundwater, coupled with concerns about the effects of climate and land-cover change on groundwater supply. Improved understanding of the impacts of watershed management on groundwater yields and management costs—particularly in the broader context of climate and land-cover change—is critical to inform these initiatives and facilitate integrated land and water management. This study develops a novel, spatially explicit groundwater hydrologic ecosystem services framework, which combines stakeholder-defined land-cover scenarios, sustainable yield estimation using a groundwater simulation optimization approach, and economic valuation, and applies it in the most heavily utilized aquifer Hawai‘i (USA). Sustainable yield estimates and resulting differences in replacement costs are estimated for six land-cover scenarios (with varying levels of urban development and watershed management) crossed with two water demand scenarios in a context of a dry future climate (Representative Concentration Pathway [RCP] 8.5 mid-century). Land-cover change is found to be an important, though less significant drive of changes in groundwater recharge than climate change. The degree of watershed protection, through preventing the spread of high-water-use, invasive plant species, is projected to be a much stronger land-cover signal than urban development. Specifically, full forest protection increases sustainable yield by 7–11% (30–45 million liters per day) and substantially decreases treatment costs compared with no forest protection. Collectively, this study demonstrates the hydrologic and economic value of watershed protection in a context of a dry future climate, providing insights for integrated land and water policy and management in Hawai‘i and other regions, particularly where species invasions threaten source watersheds.

This project developed an integrated land cover/hydrological modeling framework using remote sensing and geographic information systems (GIS) data, stakeholder input, climate information and projections, and empirical data to estimate future groundwater recharge on the Island of Maui, Hawaiʻi, USA. End-of-century mean annual groundwater recharge was estimated under four future land cover scenarios: Future 1 (conservation-focused), Future 2 (status-quo), Future 3 (development-focused), and Future 4 (balanced conservation and development), and two downscaled climate projections: a coupled model intercomparison project (CMIP) phase 5 (CMIP5) representative concentration pathway (RCP) 8.5 “dry climate” future and a CMIP3 A1B “wet climate” future. Results were compared to recharge estimated using the 2017 baseline land cover to understand how changing land management and climate could influence groundwater recharge. Estimated recharge increased island-wide under all future land cover and climate combinations and was dominated by specific land cover transitions. For the dry future climate, recharge for land cover Futures 1 to 4 increased by 12%, 0.7%, 0.01%, and 11% relative to 2017 land cover conditions, respectively. Corresponding increases under the wet future climate were 10%, 0.9%, 0.6%, and 9.3%. Conversion from fallow/grassland to diversified agriculture increased irrigation, and therefore recharge. Above the cloud zone (610 m), conversion from grassland to native or alien forest led to increased fog interception, which increased recharge. The greatest changes to recharge occurred in Futures 1 and 4 in areas where irrigation increased, and where forest expanded within the cloud zone. Furthermore, new future urban expansion is currently slated for coastal areas that are already water-stressed and had low recharge projections. This study demonstrated that a spatially-explicit scenario planning process and modeling framework can communicate the possible consequences and tradeoffs of land cover change under a changing climate, and the outputs from this study serve as relevant tools for landscape-level management and interventions.

This study investigates the community of Puerto Villamil, located on Isabela Island in the western portion of the Galapagos archipelago. Urban development and humanenvironment interactions are examined through a geographic information science perspective by (1) constructing a time-series of aerial photographs and satellite images, (2) mapping the current water and sewage infrastructure in the community using GPS and digitized analog maps, (3) assessment of the current urban setting within the context of community growth, with special reference to water quality measures at locations within and adjacent to the community, interviews and focus group discussions with health officials and local residents about water-borne disease and human health, and an analysis of the proximity of the community and its water and sewage infrastructure to the surrounding environment.

The climate science community of professionals in Hawai’i and the U.S.-Affiliated Pacific Islands is a vast interdisciplinary and international group, with the potential for spatial and sectoral barriers to communication and collaboration. This study sought to (1) assess the structural nature and expanse of climate-based communication between professionals across sectors in the Pacific Islands region; (2) identify key regional hubs and isolated groups both sectorally and spatially; and, (3) create a set of place-based tools that would increase and facilitate the connectedness of climate change resources (human, research, and adaptation). Social network analysis was chosen as a versatile method to assess the network and create free tools to facilitate future collaborations among stakeholders across spatial and disciplinary boundaries. Given the complexities of the large network, an innovative approach was used for data collection, blending a nominalist (researcher-created list of names) and realist (participant-created list in open fields) survey construction. Participants indicated frequency of communication to capture both active coworkers and periodic collaborators, consistent with the realities of the network. Survey participation was not confidential and was used to create region-wide and sub-regional maps that can be used by stakeholders to increase connectedness, in line with use-inspired science. Study results reveal a simultaneously diffuse and strongly connected network, with no isolated spatial or sectoral groups. The most central network members are those with a strong networking component to their professions. Gaps in communication were also revealed. Future research should evaluate the use and long term benefits of the created networking tools, and the specific nature of local and international communications within each sub-network.