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Colorado River Delta: Pulse Flow - One Year Later

Wednesday, April 22, 2015

The Colorado River Delta hadn’t seen regularly flowing water in 50 years.  But one year ago the U.S. and Mexico came together to work on a project to move water down the empty riverbed.

On March 23, 2014 these countries released more than 100,000 acre-feet of water into the delta below the Morelos Dam.  This area is along the Colorado River on the U.S.-Mexico border. 

On May 15, 2014, the river finally met the sea.

They did this through a pulse flow.  A pulse flow can be thought of in terms of a surge of water or a spring flood.  It is designed to represent the natural flow that keeps the river healthy. 

Image/Data Source: Bureau of Reclamation

The amount of water allocated was less than 1 percent of the river’s average annual flow but even that small amount had lasting effects one year later.

On April 14, 2015 a panel was held at The University of Arizona to discuss the impacts of the pulse flow.  The panelists included Yamilett Carrillo, the executive director of the Delta Water Trust, Francisco Zamora Arroyo, the director of the Colorado River Delta Legacy Program at the Sonoran Institute and Karl Flessa a professor in the UA department of geosciences and a co-chief scientist with the Colorado River Delta Monitoring Program. 

Carrillo said after May 15, most river conditions returned to their previous state.  “But one key feature remained,” Carrillo said.   “There are patches of green areas where you can see the impacts of the pulse flow.” 

Flessa said that the eight-week flood helped germinate and establish cottonwoods and willows that will live up to 50 years, showing that even a small amount of water can drastically affect an environment.  He also said the existing vegetation certainly benefitted from the flow. 

However, the pulse flow didn’t have a lasting impact in all of the areas. 

"In some places the pulse flow did enormous amount of good work in establishing vegetation and sustaining that vegetation. In other parts of the river it didn’t really make that much of a difference," said Flessa.

Very little of the water stayed on the surface but a lot of it infiltrated into ground.

“It is not right to call this a loss because it really is a benefit for the vegetation that lives around here, the water gets to the vegetation by the roots,” said Flessa.

Researchers are trying to map out the river and identify the prime restoration sites.  Then future efforts will be aimed in the areas that responded positively to the water flow.  

NASA/Goddard Media Studios Video Highlighting the Pulse Flow

El Niño Tracker - April 2015

Friday, April 17, 2015

This was originally published in the April 2015 Southwest Climate Outlook


Strong signals in early 2014 stalled, delaying El Niño’s onset until last month, when ocean-atmosphere coupling and an additional Kelvin wave indicated more favorable conditions. Despite this late start, El Niño continued for a second consecutive month. Recent increases in sea surface temperature (SST) anomalies (Fig.1 - 2) and ongoing convective activity associated with El Niño-favorable conditions indicate we might be witnessing a two-year El Niño event. These forecasts rely on projections during a time of increasing uncertainty, and the so-called “spring predictability barrier” continues to make it difficult to anticipate how seasonal changes will help or hinder El Niño. 

Image Source - Australian Bureau of Meteorology

Image Source - NOAA-National Climatic Data Center

The most recent forecasts continue to offer mixed signals regarding El Niño, but are more bullish this spring than last year. On April 9, the NOAA-Climate Prediction Center (CPC) issued an El Niño advisory with a 70 percent chance that El Niño will continue through summer 2015 and more than a 60 percent chance the event would last through fall.  They pointed to the large Kelvin wave, along with ongoing ocean-atmospheric coupling, as an indication a weak El Niño event would linger, with potential for further development in the long term. On April 10, the Japan Meteorological Agency declared the El Niño event likely to have ended in winter 2015, with current conditions being ENSO-neutral, but also projected El Niño conditions could return by summer.  On April 14, the Australian Bureau of Meteorology upgraded their tracker to “alert” status (one below an official El Niño designation), with warming in the tropical Pacific, weak trade winds, and projected additional ocean warming listed as contributing factors. On April 16, the International Research Institute for Climate and Society (IRI) and CPC forecasts highlighted increasingly favorable oceanic and atmospheric conditions, with an 80 percent probability of El Niño extending from summer into fall, and a 70 percent probability of El Niño extending into next winter (Fig. 3).  The North American multi-model ensemble shows a weak event extending through the spring, with potential for a moderate or even strong event by summer or early fall (Fig. 4).

Image Source - International Research Institute for Climate and Society

Image Source - NOAA-Climate Prediction Center

This El Niño event continues to defy expectations, with some models indicating conditions are strengthening rather than weakening during the spring transition.  Forecasting or characterizing this event remains difficult given the lack of analog events in the historical record, and the complexity of this El Niño guarantees it will be of interest to climatologists for years to come. Seasonal forecasts continue to indicate an increased chance of above-average precipitation through much of the Southwest, likely tied to the presence of El Niño favorable conditions. Perhaps more interesting is the possibility of a repeat of 2014’s tropical storm season, when conditions favorable to El Niño were thought to have been driving increased storm activity in the Southwest.

Southwest Climate Outlook April 2015 - Climate Summary

Thursday, April 16, 2015

Precipitation: In the past 30 days, most of the southwestern U.S. received below-average precipitation (Fig. 1). The winter wet season is wrapping up, and instead of above-average precipitation (as many of the El Niño influenced seasonal forecasts suggested), water year observations since October 1 show below-average precipitation across much of Arizona and portions of New Mexico. The situation is direr in other western regions, with California, the Pacific Northwest, and the Intermountain West recording significantly below-average winter precipitation (Fig. 2). 

Image Source - NOAA/NWS - Advanced Hydrologic Prediction Service

Image Source - NOAA/NWS - Advanced Hydrologic Prediction Service

Temperature: In the past 30 days, temperatures were above-average across Arizona and New Mexico, with anomalies between 4 to 8 degrees F above average across most of the region (Fig 3). In the six months since the water year began on October 1, Arizona, California, Nevada, Oregon, and Washington saw record-warm average temperatures (Fig. 4).

Image Source - High Plains Regional Climate Center

Image Source - National Climate Data Center

Snowpack: High temperatures and below-average precipitation led to limited snowpack across the western U.S.  As of April 16, snow water equivalent (SWE) is below average in every basin in the West (Fig. 5). In our region, SWE ranged from 0 to 32 percent of average in Arizona and 0 to 50 percent of average in New Mexico.

Image Source - Natural Resources Conservation Service - NRCS

Drought & Water Supply: The U.S. Drought Monitor highlights persistent drought conditions across the West and identifies both short- and long-term drought conditions in Arizona and New Mexico. Total reservoir storage in March was 45 percent in Arizona (same value as last year) and 26 percent in New Mexico (compared to 24 percent last year) (see reservoir storage on page 5 for details). 

Wildfire: There is potential for wildfire in any month of the year, but March through June is the windiest time of year (see page 4), which increases likelihood of red flag warning days.  This is also one of the driest times of the year, so all eyes are on fire risk potential from now through the onset of the monsoon.

El Niño: Despite a relatively late start, El Niño continued for a second consecutive month, with potential for a stronger event as we look forward towards summer and fall of this year (see page 3 for details).

Precipitation & Temperature Forecasts: The April 16 NOAA-Climate Prediction Center seasonal outlook predicts above-average precipitation this spring into summer for most of the Southwest and Intermountain West, although California and southern Arizona are notable exceptions. Temperature forecasts remain split across the region, with elevated chances for above-average temperatures along the West Coast and eastward into Arizona (and most of the western U.S.), and increased chances for below-average temperatures in western Texas and into eastern New Mexico.

Streamflow Forecasts: The April 1 forecast for the Colorado, Rio Grande, and Arkansas river basins project well below-average streamflow for Arizona and New Mexico. This pattern is repeated across much of the western U.S., especially in Utah, Nevada, California, New Mexico, and Arizona (Fig. 6), following the unusually warm and dry conditions in March. 

Image Source - Natural Resources Conservation Service - NRCS

Spring Signals the Start of Wildfire Season for the Southwest

Wednesday, April 15, 2015

A version of this post was also published in the April 2015 Southwest Climate Outlook


Flowers are blooming and trees have sprouted green leaves, signs that spring is in full swing across the Southwest and that, despite a verdant desert, wildfire season is upon us. The outlook for this wildfire season forecasts near-average wildfire activity for much of Arizona and New Mexico.

Several factors, including gradually increasing temperatures, a decreasing probability of precipitation, and increasing wind, create perfect climatological conditions for wildfire. From a climate perspective, spring is also a transition season, when the winter storm track lifts north and the sub-tropical high pressure system to the south starts to build north, both in response to an increasing sun angle and increased heating of the Northern Hemisphere. The retreat of the winter storm track and advancement of the sub-tropical ridge is generally not a clean transition, but a battle of cool and warm air masses that plays out over weeks, if not months. In this battle, the atmospheric pressure gradient tightens and wind speeds increase in response, creating conditions that can cause wildfires to grow quickly. In Arizona and New Mexico, hot, dry, and windy conditions are often the norm in late spring, and not surprisingly, this forms the heart of wildfire season for this part of the Southwest. 

Spring wildfire activity can be modulated by conditions from the previous winter, the previous summer, or even several years prior. Long-term drought conditions can stress and kill trees, increasing fire risk, but wet winters and strong monsoons can also drive increased fire risk. Fast-growing vegetation like grasses and annuals grow quickly during wet periods, then dry out and become fine fuels for subsequent wildfire seasons. 

The current wildfire outlook for the southwest notes that near-average wildfire activity is expected for much of Arizona and New Mexico, due largely to some improvements in drought conditions across the region, including above average precipitation last summer and into the early winter season. But this precipitation also spurred on new vegetation growth, increasing the risk of wildfires across southern Arizona this spring as this vegetation senesces and becomes flammable.  Fire managers will be watching these emergent conditions carefully, especially as dry and windy conditions create short-term windows of elevated fire risk.

Image Source - National Interagency Coordination Center

Image Source - National Interagency Coordination Center