Rapidly assessing the 1997 drought in Papua New Guinea using composite AVHRR imagery

Abstract

D uring 1997 P apua N ew G uinea (P N G ) experienced an intense drought. Emergency famine relief operations provided many subsistence agricultural communities with food, water and health provisions during the height of the drought. The locations of relief operations were based on a rapid and spatially explicit extensive eld survey conducted at the height of the drought for all P N G . We have tested the utility of composite Advanced Very H igh Resolution Radiometer (AVH RR) data to assist in a rapid assessment of drought conditions in P N G . Composited data were used to provide a means to overcome the frequent cloudy conditions that exist in P N G . To assess the drought we divided land surface temperatures (T s ) by the N ormalized D iVerence Vegetation Index (N D VI ). The ratio (T s /N D VI ) increases during times of drought. This is due to the increase in T s associated with more net radiation being partitioned into the sensible heat ux and the decrease in N D VI associated with decreasing amounts of plant cover. A time series of T s /N D VI is a rapid indicator of the drought at the country and province level. We calculated the integral under the T s /N D VI curve for 1997, denoted Dec Jan T s /N D VI, which allowed us to validate the assessment in two ways. F irstly, it was compared with eld-based assessments of food supply (undertaken at the height of the drought ) which classi ed areas into ve grades. P lotting Dec Jan T s /N D VI against the percentage area of each of the 14 mainland provinces experiencing food supply problems (so lives were at risk) showed a strong positively correlated relationship (r2 0.818). Secondly, for seven meteorological stations plotting Dec Jan T s /N D VI against cumulative 1997 rainfall showed an inverse relationship (r2 0.809). Both forms of validation show that the composite AVH RR T s /N D VI ratio provides a rapid means to assess drought conditions in a cloudy environment such as P N G .

Estimating Land Surface Evaporation: A Review of Methods Using Remotely Sensed Surface Temperature Data

“…Intermittent coverage makes application of TIR methods in tropical regions such as Papua New Guinea quite unreliable and impractical; though environmental metrics such as T rad /NDVI derived from monthly and longer composite AVHRR imagery have provided regional-level information about drought in such cloudy regions (McVicar and Bierwirth 2001). It also highlights the need for: (i) gap filling procedures such as described by Anderson (2007a, b); and (ii) coupling models based on TIR remote sensing with data obtained with passive microwave sensors which have lower spatial resolution but are not affected by cloud (Renzullo et al 2008).…”

Evaluation of the visible and shortwave infrared drought index in China

“…It has been widely applied in drought monitoring under the assumption that water stress is the most important factor that interferes with the plant growing process (McVicar and Bierwirth 2001;Ji and Peters 2003;Wan, Wang, and Li 2004;Wang et al 2007;Gu et al 2007Gu et al , 2008Brown et al 2008). …”

Climate change, growing season water deficit and vegetation activity along the north–south transect of eastern China from 1982 through 2006

“…The calibration based on invariant desert targets has been applied to the original data to minimize the effects of sensor degradation. The NDVI monthly data at 8 km spatial resolution was generated from previously processed biweekly NDVI composites using the maximum value compositing procedure to minimize the effects of cloud contamination (e.g., McVicar and Bierwirth, 2001). A kriging interpolation removed noise and attenuated the effect of cloudy and missing pixels for spatially-averaged NDVI of 12 natural ecosystems in NSTEC (Table 1).…”