Climate of the Paso del Norte

  • Read the full study here.

The study on climatological and meteorological phenomena of the Paso del Norte area was done to better understand the links between climate and air quality. The study was written by team members in 2012. The objectives of the study were to:

  • Summarize climatological patterns of wind, temperature, precipitation
  • Determine the sources of data should be used to track climate
  • Investigate atmospheric transport pathways to the region
  • Review phenomena that affects long-term climate variability in the region
  • Provide recommendations to improve the knowledge and tracking of climate in the region

Due to its location within the Chihuahuan Desert, the study area has an arid to semi-arid climate with mild winters, warm summers, large diurnal variations in temperature and 350 days of clear weather. The state of New Mexico has eight climate divisions, with the majority of the study area in the Southern Desert climate division. This climate division occupies an area of 18,919 square miles and is shown in Figure 1 below and covers all of Hidalgo, Luna counties and parts of Dona Ana, Grant, Sierra, and Otero counties.

Climate Region 8
Figure 1. Climate Region 8

Regional Precipitation

Annual precipitation ranges from 40 inches (102 cm) in the highest elevations of the Mogollon Mountains in the Gila Wilderness to around 9 inches (23 cm) along the Rio Grande River in southern Doña Ana county, the lower elevations in southeastern Luna and El Paso counties, and in the Tularosa Basin east of the San Andres mountain range toward the area of the White Sands gypsum dunes. The map in Figure 2 below is based on the PRISM model and shows annual precipitation averaged over the years 1971 to 2000 (Daly et al., 1994; 1997). In general, the higher elevations tend to receive more precipitation than the lower elevations. The majority of the study area averages 10 to 15 inches of annual precipitation. At the higher elevations, sites receive most of their snow between December and January with the highest accumulations measured in the Gila Wilderness. Little to no snow accumulations occur at the lower elevations in southern New Mexico.

Annual Precip in Climate Region 8
Figure 2. Annual Precipitation in Study Area

In general, fall and spring are the dry seasons, with most of the precipitation occurring in the summer from the North American Monsoon System. The numerous convective storms from the monsoon are a very important event in defining the air quality in the study region. High winds from thunderstorm downdrafts and gust fronts lofting dust into the air have accounted for many exceedances of the PM10 NAAQS in the study region. Some of the highest hourly averaged wind speeds recorded have been during these types of storms. Overall, southwestern New Mexico receives approximately 50 percent of its annual precipitation during the months of July, August and September, based on historical data from the NOAA/NWS Cooperative Observer Network The contribution from the monsoon season to annual precipitation at individual sites ranged from 48 percent (Tularosa and Lordsburg) to 58 percent (Florida in northeast Luna County).

Temperature

Based on the NOAA National Weather Service Cooperative observations, average daily maximum temperatures range from a high of 98 degrees Fahrenheit in July at White Sands to 40 degrees Fahrenheit in January at White Signal (elev. 6,070 feet) in the Big Burro Mountains northeast of Lordsburg. Average daily minimum temperatures range from nearly 69 degrees in July in Anthony to 24 degrees at the White Signal site in January.

As the map in Figure 3 below shows, mean temperatures in our study region are driven mainly by the elevation of the terrain. On a day to day basis, however, temperatures can deviate from this generalization due to patterns in air masses, temperature inversions, and effects from topography.

Mean Temperature for Climate Division 8
Figure 3. Mean Temperatures Over the Period of 1971 to 2000

Average low temperatures also are defined by elevation as shown in the map in Figure 4 below based on the PRISM model. Lowest temperatures are found in the higher elevation of the Gila Mountains north of Silver City and a few mountain tops in the Bootheel of New Mexico. An interesting feature of Figure 2.3-2 is large area of low temperatures in the range from 44.7 to 50°F in the southern portions of the region. In a few locations, some of the higher elevation terrain are at high temperatures than those at lower elevation nearby. This feature is caused by the fact that he PRISM temperature estimation methodology uses observational data. During the morning hours a stable layer near the ground creates a layer of air warmer aloft than near the ground. The temperature warming as a function of height is called a temperature inversion and this behavior is common in low lying areas such as valley floors and river channels. Since most of the climate observations in Dona Ana county and El Paso are situated in valleys, this could bias the PRISM model algorithm to create all areas with this type of lapse rate.

Minimum Temperature for Climate Division 8
Figure 4. Minimum Temperatures Over the Period of 1971 to 2000

Climate Variability

El Niño Southern Oscillation

The El Niño Southern Oscillation, or ENSO, is a natural cycle that affects sea surface temperatures, global precipitation, and wind patterns and is an example of climate variability. This cycle is described by the presence of abnormally warm or colder sea surface temperature along the equatorial region off the coast of South America toward the west to Indonesia. Normally trade winds blow winds from the east toward the west due to an area of high pressure off the coast of South America and a low over Indonesia as the top of Figure 5 below shows.

El Nino Southern Oscillation
Figure 5. Normal Pacific Ocean Sea Surface Patterns and Winds (top) and During an El Niño (bottom) (graphic from NOAA CPC)

An El Niño event occurs when the sea surface temperatures are abnormally warm in the eastern Pacific compared to the western Pacific Ocean. The warmer body of water creates warmer air above it and an area of high pressure. Winds blow from the east toward the west due to the lower air pressure from the cooler waters in the western Pacific. During La Niña events the sea surface temperatures are below normal and the cold surface water remains over central and eastern Pacific.

The El Niño Southern Oscillation (ENSO) maintains an effect on precipitation in the desert southwest mainly in the winter and spring. For example, in Doña Ana County, during El Niño events, winter precipitation averages 1.9 inches. Precipitation during La Niñas averages 1.1 inches. During the spring, an El Niño favors above average precipitation for most events in the 20th century. As Figure 6 shows, an El Niño tends to favor wetter than normal spring precipitation. The numbers in black indicate the 16 events during the 20th century in percent of normal. For the state as a whole, the past 16 events resulted in 149 percent of normal precipitation on average. The numbers in red show that the last three El Niño events before 2010 (2003, 2005, 2007) had less of an impact, with statewide average precipitation of 113 percent of normal.

ENSO New Mexico Precipitation Map
Figure 6. El Niño Spring Precipitation. Image Courtesy of Ed Polasko, NWS ABQ

La Niña events usually result in less than normal winter precipitation, particularly for the southern two-thirds of New Mexico. This is also true for spring precipitation, as Figure 7 shows. Numbers show percent of normal precipitation during La Niña events. The map on the left shows impacts of 23 La Niñas and the map on the right is for the 7 strongest La Niña events.

La Niña Spring Precipitation
Figure 7. Impacts of La Niña on Spring (MAM) Precipitation. Image Courtesy of Ed Polasko, NWS ABQ

A La Niña event is a concern in the Binational Air Quality study region due to low soil moistures and storm tracks bringing in winds but little to no precipitation. This is a recipe for potentially higher than normal dust storms and storms that are intense.

Drought

Drought manifests itself in many different ways can be classified into four major types: meteorological, agricultural, hydrological, and socioeconomic (McVicar and Jupp, 1998). You can find more in-depth descriptions of the four types here. The National Drought Policy Commission (2000) defined drought as “A persistent abnormal moisture deficiency having adverse impacts on vegetation, animals, and people.” Because there are these different types of drought and because they are all inter-related, different methods are relevant for determining the existence and impact of drought. For example, it may be sufficient to monitor precipitation and air/surface temperature to determine the extent and severity of meteorological drought, while for agricultural drought it is necessary to monitor soil moisture and vegetation conditions. In addition to these “drought” classifications, specific adverse effects of drought can be addressed. Some of the more familiar effects are loss of forage for range animals and inadequate water supplies for irrigation. Table 1 shows the drought periods in New Mexico since 1900.

Periods of NM Drought
Table 1. Periods of Drought for New Mexico calculated from the Palmer Drought Index

Extreme Events

An examination of extreme events should help us plan for the future. Extreme events can be short term like a 5-minute hail storm, a flood, or an intense dust storm; they can be stretched over a longer period of time such as a peak dry period during an intense drought. Despite the desert’s relatively calm weather, the main hazard is from flooding during torrential monsoon rains during the warm months. Looking at past records, at practically every location where there is a NWS Cooperative station, there has been a flood.

Extreme Precipitation and Flood Events

As the area along the border receives more than 50 percent of the annual precipitation during the monsoon season, we would also expect that the majority of the extreme precipitation events to also occur during that time. The month of August has the most number of days with over 2 inches of rain. The months of July, August and September have 77 percent of these extreme rain days. The years 1999, 2000 and 2006 had more than six days where at least one NWS Cooperative station in the region recorded more than 2 inches of rain. The year 2006 had the most, when 10 days of the year had more than 2 inches of rain. The wet summer contributed to 2006 having the wettest July-September on record. Over climate division 8, precipitation averaged 12.02 inches, which is 6.35 inches more than the 20th century average. Major flooding occurred in Alamogordo, Columbus, Hatch, Silver City, El Paso, Hillsboro, Vinton, Canutillo, Santa Teresa, Sunland Park, and numerous locations in Cd. Juarez in 2006. Historically notable floods have occurred in Hatch in 1988, 2002, and 2006.

Heat Waves

Even with the onset of the monsoon in that month, the warmest month of the year in climate division 8 is in July with June coming in second. Some notable warmest Junes include those in 1901, 1934, 1951, 1980, and 2003. Considering 12 Cooperative stations in climate division 8, the years 1980, 1951 and 1994 had the most number of days greater than 100°F. June of 2002 was particularly hot since there were two weeks in a row where there were 5 consecutive days over 100°F.

Winter Storms

One example of an extreme was the February 2011 cold outbreak throughout the state of New Mexico. Hardiman (2011) examined this episode and attributes this to an intense arctic air mass moving into the region along with an upper-level trough.

Human Impacts of Climate Observation

An analysis of the long-term trend in temperature is an important tool to assess the impacts of climate change in the region. It is important to look at the trends over many decades rather than over a few years since year-to-year variations in average temperature can be several degrees F. Causes for changes in temperatures can include climate change, land use change near the site, undocumented site moves, urban heat island effects and operator errors. As buildings, roads, and parking lots replace the natural landscape in populated areas, they change the heat capacity and the speed of cooling and heating. The urban heat island’s effect is to warm the urban areas more than the surroundings and potentially skew temperature records that are within the urban area. In large urban areas, the heat island effect can alter the wind flow patterns and transport pollutants from industrial areas to normally unpolluted neighborhoods.

Climate Observation Networks

The primary source of historical climate data is from the National Weather Service Cooperative Observer network. Tracking changes in precipitation and temperature in this climate division depend on a stable observational network over time. In the past few years, there has been a decrease in the number of stations in southwest NM. Of the 52 NWS Coop stations in the database in climate division 8, only 14 are currently collecting data. The number of operating stations will likely decrease over time. As a replacement of this network, NOAA has been installing two networks across the country for the purpose of collecting long-term, high quality climate data. In addition, one US Climate Reference Network site opened in September 2011 near the village of Hachita. This site is designed to measure air temperature, precipitation, solar radiation, wind speed, surface temperature and relative humidity.

Even though there are very few stations with more than 100 years of climate observations, we can use these to understand how climate has varied in this region. Even though there appears to be a sufficient number of climate monitoring stations in the climate division to assess climate change, the coverage is insufficient for monitoring and tracking health and the number of stations is likely to decrease over time. This forces the research community to rely more and more on models and the use of remote sensing to fill in the gaps. If the density of precipitation gauges is not dense enough for use in tracking extreme events, flood warnings and short term forecasting will suffer.

Recommendations

  • Make access to climate data free and accessible to the public.
  • Secure adequate funding to continue climate monitoring at the current number of stations or more.
  • Make sure that climate data from our current monitoring network is of high quality and lessening data gaps.
  • Expand the CoCoRaHS precipitation observer network into rural areas in the study area. A small amount of funding would be needed to purchase rain gauges to lessen the burden on the volunteer observers and offer training.
  • Continue funding for long-term climate monitoring at Columbus.
  • Expand emergency roadway monitoring along major roads where blowing dust is a hazard. Here there needs to be collaboration with public safety, NM Department of Transportation, counties, and local roads authorities. These would require reliable telemetry to get data on sub-hourly basis. At these stations, there is also need for measuring dust levels.
  • Metadata to document the data and any changes to the data but also to the surrounding environment at the station and around the immediate location.
  • Seek partnerships between state/federal/local agencies to combine efforts.

References

Daly, C., R.P. Neilson, and D.L. Phillips. (1994). A statistical-topographic model for mapping climatological precipitation over mountainous terrain. J. Appl. Meteorol., 33:140-158.

Daly, C., G.H. Taylor, and W.P. Gibson. (1997). The PRISM approach to mapping precipitation and temperature. In In reprints: 10th Conf. on Applied Climatology, Reno, NV. American Meteorological Society, Boston, MA, pp. 10-12.

Hardiman, T. (2011). Intense cold wave of February 2011, National Weather Service, Santa Teresa Forecast Office. Available at http://www.srh.noaa.gov/images/epz/Storm_Reports/Cold11/Feb2011ColdWx.pdf

McVicar, T.R. and D.L.B. Jupp. (1998). “The Current and Potential Operational Uses of Remote Sensing to Aid Decisions on Drought Exceptional Circumstances in Australia: a Review”, Agricultural Systems, Vol. 57, No. 3, 399-468.

NDPC (2000). Preparing for Drought in the 21st Century. Report of The National Drought Policy Commission. May 2000