# Presentation: 451798

## Developing Land Use Change – Climate Change Scenarios

- For Central America

- Presented by Bob Oglesby, NASA/MSFC

## Project Hypothesis:

- Deforestation and other land use changes currently occurring
- in Central America have a profound, and in many cases
- detrimental effect on the hydrologic cycle, increasing the
- probabilities of both devastating droughts and floods.

- The goal of this research is to understand the effects of human activity
- upon the hydrological processes over Central America in order to
- understand and so ultimately forecast climatic effects for decision
- making by scientists, educators, and policy-makers.

## KEY QUESTIONS:

- How significant to Central American climate change is deforestation / land use change in comparison to natural climate variability?
- What role do these anthropogenic factors play in floods and droughts?
- What are possible future scenarios of climate change resulting from greenhouse gas
- increases and how do they compare to changes projected to result from deforestation
- and other land use changes?

## Deforestation is not the only agent of climate change over Central America. Globally, warming of surface temperatures, with associated changes in the hydrologic cycle and other important aspects of climate, is thought to be occurring due to the steady rise in greenhouse gases (GHG’s). 

**Indeed, deforestation has a direct impact on this by causing an overall net release of **
**GHG to the atmosphere**** **
**But how will these future climate changes affect Central America? Will deforestation make them worse? Or conversely, will the climate changes help ameliorate the impacts of deforestation? **

## Though these effects are very difficult to quantify, and hence predict, it is my

- personal belief that the recent floods and landslides in southern Mexico, El
- Salvador, and especially Guatemala were exacerbated, if not directly caused,
- by deforestation of very steep hillsides.
- The rain that fell has been described as a steady, moderate rain, people
- apparently were caught by surprise by the extent of the flooding and land-
- slides.
- If the hillsides had been forested, much more of this rain could have been
- caught and absorbed. It would have been released more slowly into streams,
- and the hillsides themselves more likely would have remained stable.
- Again, this is my personal conviction which I cannot at this time prove.

## We have already performed some preliminary studies relevant to our proposed research. 

**We have already performed some preliminary studies relevant to our proposed research. **
**This prior work has provided two key insights: **
**We have shown that a regional climate model (the NCAR/PSU MM5) does a credible job at simulating at least precipitation over Central America. **
**We have shown that complete deforestation of Central America has the potential to have major impacts on temperature and precipitation. This experiment was meant to be an ‘end-member’ test to bound the possible climate impacts. **
**We suspect other facets of the hydrologic cycle, e.g., evaporation and runoff, will also eventually be shown to be similarly impacted.**

## Slide 7

## Slide 8

## The next slide shows the impact of human activities on climate, especially as they impact drought. 

- The next slide shows the impact of human activities on climate, especially as they impact drought.
- We made two runs using the MM5 regional climate model. One run had all of Mesoamerica containing evergreen forest, while the other run had all of Mesoamerica containing grassland.
- Replacing trees with grassland has two major effects:
- 1. an increase in albedo, leading to cooling and stabilization of the atmosphere
- 2. a large reduction in evapotranspiration from the surface, leading to warming and stabilization of the atmosphere. The reduction in evapotranspiration overwhelms the increase in albedo, leading to warmer surface conditions.
- But both processes tend to stabilize the atmosphere and reduce precipitation

## Mesoamerican Deforestation Scenarios – Implications for Wet and

**Mesoamerican Deforestation Scenarios – Implications for Wet and**
**Dry Seasons**

- January (dry season)
- Temperature (left) –
- warms everywhere
- but only by 1-2deg C
- Rainfall (right) - little
- impact as it’s the dry
- season!

- July (wet season)
- Temperature (left)
- warms everywhere,
- but now as much as
- 2-5 deg C.
- Rainfall (right) shows
- a decrease of 20-30%
- over much of the
- Mayan region

## We see warming and drying in both the dry and wet seasons, but the impact is 

**much greater in the wet season for both temperature and rainfall. **
**These results suggest that human activities in this region could help trigger, **
**prolong, or exacerbate drought.**

## The next slide shows the possibility of natural drought. 

- We show time series of warm season rainfall (defined as rain from June 1 through September 30) as averaged over the Mayan lowland region of Guatemala and the Yucatan. The rainfall was simulated by a global climate model, the National Center for Atmospheric Research CCSM3.

## This plot shows rainfall over the Maya 

- This plot shows rainfall over the Maya
- ‘lowland’ region for the ‘wet’ season
- (June-September) for 100 years of
- ‘present-day’ conditions as simulated
- by a global climate model.

- This plot shows rainfall for the wet
- season for a model simulation of the
- period 1870-1999.
- Note much more prolonged periods
- of drought, e.g., 1952-1981, during
- which 24 of 30 years have below
- average rain.

## The plot on the left is from a 100 year ‘present-day’ control run, that is with present-day conditions run over and over again for 100 model years. We see many dry periods, though only a few extend for more than a few years. 

- The plot on the right is from a run for the period 1870-1999, that is, all appropriate forcings (e.g., changes in solar irradiances, greenhouse gas increases, aerosols, volcanoes, etc.) for this period.
- They key difference is that now we see some prolonged periods of dry conditions, including one period of 24 out of 30 years being dry
- These results suggest that naturally-occurring drought can wreak havoc on this region. The key questionis whether human-induced land use changes can make these droughts worse, or occur more frequently!!

## The next step is to modify the current land surface classification according to the estimates of present-day (circa 2002) deforestation and other land use changes. 

- We will also make runs projecting rates of deforestation forward for up to 20 years into the future.
- That is, we will make model runs with more realistic scenarios of deforestation (and other land use changes).
- The land use classification portion of the SERVIR project will provide us with the present-day landuse classifications.
- In conjunction with our Central American partners, we need to come up with likely future scenarios of land use changes.
- (To help accomplish these, I have been spending time in the land use workshop being held
- Concurrently with ours.)