Mohave Generating Station to the west were similarly found to affect visibility in the canyon. The plant was required to have installed SO2 scrubbers, but was instead shut down in 2005, completely eliminating its emissions. Prescribed fires are typically conducted in the spring and fall in the forests adjacent to the canyon to reduce the potential for severe forest fires and resulting smoke conditions. Although prescribed fires also affect air quality, the controlled conditions allow the use of management techniques to minimize their impact. Climate change Due to the increase of greenhouse gases, temperatures have steadily risen making recent years the warmest of the century. Temperatures have increased in Arizona by 2.1 degrees Fahrenheit since 1895. From 1916–2014, naturalized streamflow in the Upper Colorado River Basin decreased by 16.5%, in spite of a slight increase of +1.4% in annual precipitation over the same period. Increases in temperature correlate to increased evaporation, loss of reflective snow, and decreases in snowpack, reducing available water in the Colorado River by an estimated 9.3% per degree Celsius of warming. Over the last 30 years, the South Rim of the Grand Canyon has averaged 13.4 inches of rainfall per year, while the North Rim has averaged 24 inches. The first dual distribution water system in the United States was built on the South Rim, treating and reclaiming wastewater for nonpotable reuse as early as 1926. Early on, water for human use was brought in by tankers, and pumped up from a spring deeper in the canyon. In the 1960s, the Transcanyon Pipeline was built to carry water from the North Rim down into the canyon and back up to the South Rim. Every day 500,000 gallons of water are pumped from underground springs on the North Rim through the pipeline to supply the more heavily developed South Rim with water. As water consumption continues to soar due to increasing visitation in the park, both the sustainability of the water supply and the condition of the pipeline are in question. As of 2019, plans to replace the aging 16-mile aluminum pipeline were proposed. Another proposal, from the Bureau of Reclamation, recommended that the park drill a well into the Redwall-Muav aquifer to meet the increasing water consumption. However, the aquifer's recharge rate stands to decline over time due to decreases in precipitation and snowpack. Some effects of over pumping aquifers include land subsidence, reduction in rivers