Climate, Drought, and Wildfire Effects on Water Quality

Recent Conditions and Short- Term Forecast

Historical Drought in the Southwest  Palmer Drought Severity index  Soil moisture availability  Incorporates Precipitation, most important Temperature Soil conditions  Includes time lags If it’s been dry for months, a single rainstorm will not change drought to wet  Negative PDSI = dry, positive PDSI = wet

Pacific Decadal Oscillation  Regular pattern of high and low pressure systems over the northern portions of the Pacific Ocean.  20- to 30-year time scale, and correlates with relatively wetter or drier periods in the western portion of North America.  Positive PDO phases tends to enhance El Niño conditions and weaken the effects of La Niñas.  Negative PDO phases enhance the effects of La Niñas and weaken the effects of El Niños

PDO PhaseNorth Pacific Sea Surface Pressure North Pacific Sea Surface Temperature Influence on El Niño Conditions Influence on La Niña Conditions PositiveLowColdEnhanceWeaken NegativeHighWarmWeakenEnhance

Less Snow, Less Water: Climate Disruption in the West. Rocky Mountain Climate Organization, 2005 “What this work shows is that, even with a conservative climate model, current demands on water resources in many parts of the West will not be met under plausible future climate conditions – much less the demands of a larger population and a larger economy” Dr. Tim Burnett, “The Effect of Climate Change on Water Resources in the West: Introduction and Overview”

Likely Effects of Climate Disruption in the West  More Heat Likely to be greater in winter than summer  Smaller Snowpacks Winter precipitation may be more likely in the future to fall as rain rather than snow.  Earlier Snowmelt Warming earlier in the year may melt snowpacks sooner  Increased evaporation Increased soil dryness and evaporation from rivers and reservoirs

It’s Not Just the Drought, it’s the Heat

Snowpack Losses in the Colorado River Basin  Predicted losses of 24% by  Up to 30% by  Snowpack has been below average for 11 of the last 16 years.

What About Last Winters Precipitation?  Brought a slight reprieve from sustained drought conditions in water year  Shortage risk has been “rolled back” by about one year.  System reservoir storage is currently about what it was in  The entire Colorado River storage system decreased from 55.7 (95% capacity) to 29.7 (52% capacity) MAF from October 1, 1999 to October 1, 2004.

In Light of All This…  The sky is not falling.  Climate is highly variable with the only constant being variability.  Evidence of drought and climate change are likely occurring at a faster-than- anticipated rate.

This puts added importance on cohesive, comprehensive, and pro- active planning by water resource management agencies to ensure adequate water supplies for the foreseeable future.

Effect of Climate and Drought on Wildland Fires  We initiated this project prior to the Rodeo- Chedeski fire in  We were the ones to mention, and predict, long-term impacts to downstream reservoirs.  Most of these predictions have proven to be true and the reservoirs still suffer from this “re- setting” event.

Pre- and Post-fire Nutrient Loading

Increasing Hypolimnetic Anoxia in Roosevelt

Heat and Drought Effects on Vegetation

Not All Wildfires are Created Equal…  The amount of suspended sediment delivered to a river or reservoir following a wildfire depends upon several factors including local topography and vegetation type.  Some vegetation types have adapted to wildfire and require it as part of its natural succession.  Others, such as the Sonoran Desert, have likely never experienced wildfires like we have seen the last few years.

Cave Creek Complex and Rodeo-Chedeski Fires  Different type and amount of fuel consumed.  Rodeo-Chedeski: Huge amount of ground fuel built up for decades. Intense, high heat fires volatilize nutrients and destroy roots, tubers, and rhizomes beneath the surface. Re-vegetation will take years – decades even with intense re-seeding efforts.  Cave Creek Complex: Oak, chaparral, brushes and grassland vegetation have evolved with frequent fire and require it for succession.

Wildfire and Invasive, Non- Native Plant Species  The Cave Creek Complex Fire started in the Sonoran Desert.  The Sonoran Desert never saw fire until the 1970’s when invasive plants began filling in spaces between native species.  Cave Creek Complex Fire was carried by red brome and started in an area that had previously burned the year before!

 Native desert plants have no adaptation to wildfire.  Native plants, even when a wet winter increases their numbers many fold, lack the biomass of invading, non-native species and rarely burn.  The spread of non-native, invasive plant species is exacerbated by increasing drought, warm winters, and increasing heat and climate change.

 Increased frequency of fire in the Sonoran Desert, kills native species and non-natives are quick to fill this niche.  The Sonoran Desert will likely look very different in a few decades and more closely resemble a savannah.

Watershed and Water Quality Implications  From a water quality standpoint, the real danger lies in having fires start with increased frequency at lower elevations and then spreading into higher elevations consuming more biomass and increasing in intensity.  Watershed vegetation is the “sponge” that keeps water flowing in streams and rivers and, eventually, flowing into reservoirs.

Summary  There will likely be changes in both water quantity and quality delivered to the Valley in the future.  The best way to ensure we have the tools needed to document these changes is through continued data acquisition.  Climate change and drought are linked to biological, physical, and chemical factors which directly affect water quantity and quality delivered to the Valley.

Questions?