Jonathan A. Patz

Footnotes See also Reviews p 1323 Competing interests None declared.

Connections between weather and disease are well established, with many diseases occurring during certain seasons or erupting from unseasonable flood or drought conditions. With new concerns about global warming, accompanied by greater climate variability, many recent studies have focused on disease fluctuations related to short-term or interannual climate oscillations (e.g., from weather extremes driven by El Niño). Yet, the nagging question remains as to whether or not there has been any documented change in human disease trends in response to long-term climate change, since warming has already occurred over the last century (1, 2). This study likely represents the first piece of evidence that warming trends over the last century are affecting human disease. This trend analysis has been elusive because of the scarcity or inconsistent quality of health databases over long periods. Additionally, strong confounding factors especially complicate long-term trend analysis. Some of these include increasing trends in travel, trade and migration, erratic disease control efforts, emerging drug or pesticide resistance, human population growth, urban sprawl, agricultural development, and variable reporting biases. But Rodo et al. (3) have now succeeded in finding a robust relationship between progressively stronger El Niño events and cholera prevalence in Bangladesh, spanning a 70-year period; their use of a uniquely high quality extensive cholera database and innovative statistical methods were key. This study likely represents the first piece of evidence that warming trends over the last century are affecting human disease. The investigators used innovative statistical methods to conduct a time-series analysis of historical cholera data dating back to 1893 to examine the effect of nonstationary interannual variability possibly associated with climate change. In the last two decades, the El Niño Southern Oscillation (ENSO) differed from previous decades (3). Since the 1980's, there has been a marked intensification of the ENSO beyond that …

A semidistributed watershed model is applied over the Mahantango Creek catchment in Pennsylvania to estimate future changes in direct runoff under 22 different climate scenarios. It is shown how different subcatchments of the watershed may respond to possible changes in the precipitation and temperature regimes. Subcatchments with the most unfavorable future runoff responses can be identified where possible changes in land use management practices may be suggested.

Reactive-nitrogen (Nr) has a wide variety of beneficial and detrimental effects on human health. The most important of the beneficial effects are increasing global and regional food supplies and increased nutritional quality of available foods. However, lack of adequate dietary intake of amino acids and proteins is a serious cause of malnutrition when food supplies are inadequate because of poverty, drought, floods, wars, and displacements of people as refugees. There is sufficient, though limited, quantitative data indicating that increased circulation of Nr in the environment is responsible for significant human health effects via other exposure pathways. Nr can lead to harmful health effects from airborne occupational exposures and population-wide indoor and outdoor air pollution exposures to nitrogen dioxide and ozone. Nr can also affect health via water pollution problems, including methemoglobinemia from contaminated ground water, eutrophication causing fish kills and algal blooms that can ...

Disturbances of climatic and ecological systems can present risks to human health, which are becoming more evident from health studies linked to climate variability, landuse change and global climate change. Waterborne disease agents, such as Giardia cysts and Cryposporidium oocysts have been positively correlated with rainfall. El Niño-related extreme weather conditions can have a significant impact on vector- and water-borne diseases. The linkages between weather, terrestrial ecology and human health have been discovered for some diseases, such as rodent-borne hantavirus. Marine ecology also plays a role in determining human health risks, such as from cholera, and other enteric pathogens. Deforestation and ensuing changes in landuse, human settlement, commercial development, road construction, and water control systems singly, and in combination have been accompanied by increases in or emergence of diseases like malaria and schistosomiasis in some regions of the world. Long-term climate change may increase the frequency of heat waves and potentially air pollution episodes, increase the number of extreme weather events, cause coastal flooding and salination of fresh water aquifers, and displace coastal settlements. Ultimately, a two-pronged approach (empirical and modeling studies) is required to better understand these linkages between climato-logical and ecological change as determinants of disease.

Objectives. Rainfall and runoff have been implicated in site-specific waterborne disease outbreaks. Because upward trends in heavy precipitation in the United States are projected to increase with climate change, this study sought to quantify the relationship between precipitation and disease outbreaks. Methods. The US Environmental Protection Agency waterborne disease database, totaling 548 reported outbreaks from 1948 through 1994, and precipitation data of the National Climatic Data Center were used to analyze the relationship between precipitation and waterborne diseases. Analyses were at the watershed level, stratified by groundwater and surface water contamination and controlled for effects due to season and hydrologic region. A Monte Carlo version of the Fisher exact test was used to test for statistical significance. Results. Fifty-one percent of waterborne disease outbreaks were preceded by precipitation events above the 90th percentile (P = .002), and 68% by events above the 80th percentile (P = .001). Outbreaks due to surface water contamination showed the strongest association with extreme precipitation during the month of the outbreak; a 2-month lag applied to groundwater contamination events. Conclusions. The statistically significant association found between rainfall and disease in the United States is important for water managers, public health officials, and risk assessors of future climate change.