Multitemporal remote sensing analysis of a playa lake groundwater system in northern Chile

GIS in Water Resources, Fall 2011Katherine Markovich

What is a playa lake or salar, and why do we care?Playa lake: an arid zone feature that is transitional between a playa, which is completely dry most of the year, and a lake (Briere, 2000).

In this study, a salar is an internally drained evaporative basin with surface water occurring mostly from spring discharge.

Image courtesy of Wikimedia Commons

Keller and Soto, 1998

1) Can we use remote sensing to quantify surface water extent on the salars?

2) Can we validate/refute Pastos Grandes as the recharge zone for Ascotán?

3) Can we determine if pumping has affected the northern springs and/or the springs at Carcote?

Research Questions

Proposed regional groundwater system:

Hypothesis: Yes, remote sensing is useful for monitoring of remote areas over large spatial and temporal scales. In situ field data can supplement the remote sensing analysis.

HydrologyΔV= (P+IGW+ISW) – (ET+OGW+OSW)

Background

( ) + assumptions =

Simple water budget for salars: ΔV= (IGW) – (E+OGW)

∆V=change in volume

P=precipitation (rain/snow)

ISW=surface water inputs

IGW=groundwater inputs

ET=evapotranspiration

OSW=surface water outputs

OSW=groundwater outputs

Remote sensing gives us ΔA, which can be related to the groundwater system!

Methods

Landsat Processing

Landsat 4-5 TM and 7 ETM+- 7-9 bands- 30m pixel resolution- Cloud-free- Orthorectified- Georeferenced

1) Download from USGS Landsat Archive

2) Stack, project, clip using ESRI ArcGIS 10

-WGS 1984 Datum-UTM Zone 19S Projection-Nearest Neighbor Resampling

3) Classify water pixels using ERDAS Imagine 2011

-Convert to water extent-Quality control-Perform analysis with respect to climate, chemical, and pumping data

Results

Optical Analysis• ‘False’ image• Qualitative only

UnsupervisedClassification

• Casteñeda et al., 2005• Depth/salinity

SupervisedClassification

• A priori knowledge• Possible Volume

1) Can we use remote sensing to quantify surface water extent as an analog to the regional groundwater system?

NDWI

• Xu, 2006• Overestimates

Results

Initial Multitemporal Analysis for 2009

January DecemberJulyMayMarch

Nov-08 Dec-08 Feb-09 Mar-09 May-09 Jul-09 Aug-09 Oct-09 Dec-09 Jan-100

2

4

6

8

10

12

0

20

40

60

80

100

120

140

160

180

200

2009

Avg. Precip.

Area

(km

2)

Prec

ipita

tion

(mm

)

Results

2 3 4 5 6 7 8 9 10 110

10

20

30

40

50

60

70

f(x) = 4.04073367075551 x − 3.87097007587574R² = 0.227565475064766

Salar Water Extent (km2)

Cald

era

Wat

er E

xten

t (km

2)

2 3 4 5 6 7 8 9 10 110

5

10

15

20

25

30

35

40

f(x) = 3.43872406035703 x − 4.67418784927699R² = 0.848797995379205

Salar Water Extent (km2)

Cald

era

Wat

er E

xten

t (km

2)

August, 1985 August, 1990

2) Can we validate/refute Pastos Grandes as a recharge zone for Ascotán?

Jan-85 Sep-87 Jun-90 Mar-93 Dec-95 Sep-98 Jun-01 Mar-04 Nov-06 Aug-090

2

4

6

8

10

12

f(x) = − 0.000431037530626917 x + 20.9791231775032R² = 0.40884261132233

TotalLinear (Total)North AscotanSouth AscotanCarcote

Sala

r Wat

er E

xten

t (km

2)Results

3) Can we determine if pumping has affected the northern springs and ultimately the water extent at Carcote?

CAR-1

V2

V7

V10

V11

¯

0 2.5 5 7.5 101.25Kilometers

LegendField Sites

Salars

North Ascotán

Carcote

South Ascotán

1) Developed a methodology to quantify surface water extent .

2) Found a positive correlation between the Pastos Grandes caldera and water extent on the salars.

3) Total surface water extent has decreased since 1985, but it is not certain whether the cause is predominantly anthropic or climatic.

4) Carcote shows a muted response to the changes at Ascotán, but the hydrologic relationship between North and South Ascotán remains a question.

Summary

Future Work:1. Continue remote sensing analysis by adding images, attempting to quantify volume,

and addressing uncertainty.

2. Further analysis of meteorological, hydrochemical, and pumping data from El Abra records and lab results.

3. Possible precipitation modeling using NASA TRMM data

Questions?