Malaria & Bioclimate indices

by Dipanwita Ghosh Sarkar (contact: ghosh_sarkar.dipanwita@uqam.ca)

Indices List:

Malaria Indices: Number of consecutive days with daily mean temperature above \(18^{o}C\). (Data Used: Era5 land \(0.1^{o}\))
Bioclimate Indices:
- BIO01-BIO19: ERA5 (Period: 2006-2022; Resolution: \(0.25^{o}\))
- BIO20-BIO35: CORDEX Models (Period: 2006-2099/2100; Resolution:\(0.25^{o}\))

Malaria Indices:

Event: Detect the time spans when daily average temperature was above 18°C for consecutive 30 days for each grid over North America.
Frequency: Per year how many times did the event occur.
Data: Era5-land data for 1950-2023,August 25(\(0.1^{o}\)).

Methodology:

1: From time series of each grid, consecutive days with daily mean temperature \(18^{o}C\) or above was accumulated to find the desired time block for each grid.
2: Area averaged Time series of daily mean temperature was calculated over the main land of United States(US) and Canada and from the time series the indices were calculated by accumulating the consecutive days with daily mean temperature above or equal to 18°C.
3: To understand the changes over decades the whole period was divided into 8 decades as following.

Decades Definition:

Decade 1: 1950-1959
Decade 2: 1960-1969
Decade 3: 1970-1979
Decade 4: 1980-1989
Decade 5: 1990-1999
Decade 6: 2000-2009
Decade 7: 2010-2019
Decade 8: 2020-2023

Example of events per grid for 2023 over North America:

Indices over North America (Resolution: 0.1°)

Areas over which the time series was calculated:

………………………………………………………………

Case 1: US

Indices derived from Area Averaged time series over US

Trend per event for US.

## 
##  Mann-Kendall trend test
## 
## data:  (final_indices$length)
## z = 3.409, n = 72, p-value = 0.000652
## alternative hypothesis: true S is not equal to 0
## sample estimates:
##            S         varS          tau 
## 7.010000e+02 4.216367e+04 2.793865e-01

In this output the \(\tau\) value is 0.2794 which indicates a moderate, monotonic increase in yearly length of the events over the 73 year time period. This degree of positive monotonicity is significant with the p-value of 0.000652. The limitations of this test in the trend analysis sense is that it does not provide any insight into the magnitude of the trend. This can be informed by Sen’s Slope testing.

## 
##  Sen's slope
## 
## data:  final_indices$length
## z = 3.409, n = 72, p-value = 0.000652
## alternative hypothesis: true z is not equal to 0
## 95 percent confidence interval:
##  0.08510638 0.29032258
## sample estimates:
## Sen's slope 
##      0.1875

So the length of events per year has a significant upward trend of magnitude 0.187 per year for US.

The visualization shows a hike in the length of events after \(5^{th}\) decade.

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Case 2: Canada

Trend per event for Canada.

## 
##  Mann-Kendall trend test
## 
## data:  df_can$length
## z = 4.0822, n = 66, p-value = 4.462e-05
## alternative hypothesis: true S is not equal to 0
## sample estimates:
##            S         varS          tau 
## 7.380000e+02 3.259533e+04 3.477227e-01

## 
##  Sen's slope
## 
## data:  df_can$length
## z = 4.0822, n = 66, p-value = 4.462e-05
## alternative hypothesis: true z is not equal to 0
## 95 percent confidence interval:
##  0.1785714 0.4583333
## sample estimates:
## Sen's slope 
##   0.3243243

Interpretation of both Mann-Kendall test and Sen’s slope indicates a monotonic and significant (p-value=4.462e-05) increasing trend in the length of events over Canada for last 7 decades.The slope value 0.324 indicates a moderate rate of increase of the time block.It can be summarized visually from the above figure that the time block started expanding it’s length after July,1978.

The increase of length of time block started occurring since \(4^{th}\) decade of the study period.

The plots clearly show an increasing trend in data ranges and median values. In the density distribution plot with increasing decades the distribution gets shifted towards higher values.

………………………………………………………………………………

Extracting Months:

Finding month for which most number of grids had average temperature above or equal to \(18^{O}C\) for consecutive 30 days.

Spatial presentation of months with temperature 18°C.

…………………………………………………………………………………

BIOCLIMATIC INDICES:

BIOCLIMATIC INDICES FOR NORTH AMERICA FOR CORDEX MODELS (Resolution: 30 km)

BIOCLIMATIC INDICES FOR NORTH AMERICA ERA5 (Resolution: 30 km)

References

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S.M. Vicente-Serrano, S. Beguería, J.I. López-Moreno. 2010. A Multi-scalar drought index sensitive to global warming: The Standardized Precipitation Evapotranspiration Index – SPEI. Journal of Climate 23: 1696, DOI: 10.1175/2009JCLI2909.1.