Rainfall Spatial and Temporal Distribution in Sumber Jaya,

West lampung

Rita Manik

Back ground

• There was environmental degradation in Sumber Jaya, including the flood in February 2002 that damaged the power plant and causing a serious shortage of electricity in Lampung Province as well as periodic water deficits needed to drive the turbines during the dry season

• Preservation of watershed functions and erosion control are the two major arguments for retaining forests in Sumber Jaya as protection areas

• Local governments blamed coffee farmers for the problems. Such accusations create conflicts between local forestry officers and villagers who claim that the previous government officials officially transferred some parts of the land within the forest zone to them and they have the right to manage the lands as they wish

Rainfall distributions

VS

Land use changes

Natural forrest

VS

Agroforrest

Problems

•Rainfall – runoff relationship in catchment scale

The rainfall--runoff relationship quantifies the response function describing the behaviour of a watershed. The response function is a result of numerous processes, complex and interdependent, that participate in the transformation of rainfall into runoff (Singh and Birsoy, 1977).

Water inputRainfall Watershed Water discharge

output

Rainfall distribution

• Temporal distribution

• Rain depth

• Spatial distribution

Research site

Methods

Nested catchments

Catchment Area (ha) Mean slope (%)

1 2.84 29

2 8.21 46

3 12.39 33

4 20.45 20

5 27.22 26

WB 67.68 26

FR 10.39

AF 4.39

Rain gages

Parshall Flumes

Methods

• Rainfall temporal distribution:

cross-correlations

auto-correlations

• Rainfall spatial distribution :

cross-correlations

Kriging

Rainfall temporal distribution:2 August 2005

-0.5

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

Time (9:00)

Rai

nfa

ll (m

m)

C!

C3

AF

C5

WB

FR

23 October 2005

-0.5

0

0.5

1

1.5

2

2.5

3

0 50 100 150

Time(16:00)

Rai

nfa

ll (m

m)

C1

C3

AF

C4

C5

WB

25 October 2005

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

0 50 100 150 200 250

Time (16:00)

Rai

nfa

ll (m

m)

C1

C3

AF

C4

C5

WB

FR

26 October 2005

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

0 100 200 300

Time (11:00)

Rai

nfa

ll (m

m)

C1

C3

AF

C4

C5

WB

FR

Rainfall temporal distribution:2 November 2005

0

0.5

1

1.5

2

2.5

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43

Time (14:00)

Rai

nfa

ll (m

m)

C1

C3

C4

C5

CAF

CFR

CWB

19 November 2005

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

0 100 200 300

Time (11:00)

Rai

nfa

ll (m

m)

C1

C3

C4

C5

AF

WB

FR

7 December 2005

-0.5

0

0.5

1

1.5

2

2.5

3

0 100 200 300 400

Time (12:00)

Rai

nfa

ll (m

m)

C1

C3

C4

C5

AF

WB

FR

Daily Average of coefficient correlation among catchments

Date C1 C3 C4 C5 CAF CFR

16-Jul-05 0.298345 0.403841   0.459069 0.307098 0.190206

18-Jul-05 0.510047 0.466725 0.574263 0.244129 0.443542

19-Jul-05 0.952486 0.960662 0.97749 0.973713 0.931874

02-Aug-05 0.440578 0.368632 0.522944 0.263833 0.313566

21-Aug-05 0.471879 0.24392 0.517687 0.314581 0.292299 -0.04579

22-Aug-05 0.777705 0.782464 0.745109 0.652387 0.572682 0.413579

25-Sep-05 0.781395 0.764145 0.804101 0.699094 0.588346 0.205309

18-Oct-05 0.712814 0.722281 0.701596 0.582218 0.393156  

22-Oct-05 0.566868 0.696074 0.622975 0.509745 0.329756  

23-Oct-05 0.584093 0.530136 0.44626 0.169781 0.258088  

25-Oct-05 0.72363 0.634489 0.607306 0.435997 0.47959 0.257356

26-Oct-05 0.839183 0.750404 0.735457 0.605203 0.360082

03-Nov-05 0.45747 0.673518 0.610762 0.441547 0.172871  

18-Nov-05 0.684072 0.720389 0.697829 0.640743 0.340826  

19-Nov-05 0.70919 0.646349 0.453432 0.558036 0.395826  

20-Nov-05 0.434234 0.470342 0.151299 0.299228 0.114708 -0.33936

25-Nov-05 0.664426 0.649788 0.621162 0.578245 0.411551 0.081998

27-Nov-05 0.510451 0.498357 0.525282 0.278741 0.195067 -0.03525

07-Dec-05 0.718757 0.65773 0.520478 0.509883 0.469442 0.199205

08-Dec-05 0.585608 0.555513 0.475366 0.425176 0.065773  

27-Dec-05 0.63306 0.689996 0.607875 0.535225 0.31452  

02-Aug-05

  C3 CAF C5 CWB CFR

C10.48185

90.68351

60.54337

60.39274

8 0.437479

C3  0.38786

50.54506

60.56494

4 0.278007

CAF    0.35065

60.32881

5 0.199111

C5      0.39685

9 0.745667

CWB         0.315157

23-Oct-05

  C3 CAF C4 C5 CWB

C10.6966

420.8079327

20.8447

110.3103

860.4557

9

C3  0.7389997

90.7407

70.3685

50.5921

55

CAF    0.8210

420.2944

930.4879

75

C4      0.2742

450.4540

6

C5        0.2117

04

Time lags

  16-Jul-05 18-Jul-05 02-Aug-05 21-Aug-05

Lags WB FR CAF CFR CAF CFR FR WB

2 0.7853 0.8572 0.5175 0.5844 0.7840 0.8808 0.5852 0.1295

4 0.6868 0.7792 0.4265 0.4194 0.5935 0.7379 0.4935 0.4942

6 0.5955 0.6960 0.2270 0.1818 0.4816 0.5840 0.1523 0.3324

8 0.3977 0.5764 0.1841 0.1393 0.4774 0.4358 0.2176 0.2163

10 0.2979 0.4876     0.4776 0.2909 0.0324 0.2771

12 0.1825 0.3701     0.4776 0.2127 0.0098 0.3084

14 0.0819 0.2354     0.3857 0.1825 -0.1305 0.0795

16 0.0802 0.1274     0.3535 0.1918 -0.2155 0.2472

18         0.3369      

20         0.3282      

22         0.2557      

24         0.2737      

26         0.2267      

28         0.1634      

Time lags

  22-Aug-05 25-Sep-05 18-Oct-05 23-Oct-05

Lags CFR CWB CFR CWB CAF CAF C5 CWB

2 0.8053 0.5692 0.8591 0.7319 0.6791 0.7696 0.7500 0.8213

4 0.6376 0.2506 0.7027 0.4579 0.5344 0.7084 0.5291 0.6525

6 0.4661 0.1173 0.5119 0.1510 0.4826 0.5764 0.3124 0.4779

8 0.3145 0.1015 0.3328 -0.0115 0.3940   0.1729 0.3322

10     0.1388 0.0841 0.2051   0.0992 0.2435

Spatial Distribution

Average of coefficient correlation among catchments

  C3 C4 C5 CAF CFR CWB

C1 0.721266 0.671723 0.777534 0.751575 0.384678 0.535187

C3   0.618752 0.807045 0.764234 0.253727 0.715793

C4   0.686781 0.601693 0.199235 0.334294

C5   0.714603 0.315822 0.637122

CAF   0.288417 0.550781

CFR   0.206051

             

02-Aug-05

Sill Length Centre

2.0043 0.45  

1.2383 0.0925  

1.3747 0.0925  

1.3163 0.45 C1 

1.3344 0.45 C1

1.0302 0.45 C1

1.1034 0.45 C1

0.3653 0.45 C1

0.7158 0.0925  

0.7158 0.0925  

1.7465 0.0925  

1.875 0.0925  

25-Sep-05

Sill Length Centre

1.1976 0.0925  

1.5532 0.0925  

0.8655 0.0925  

1.857 0.0925  

1.7579 0.0925  

1.8733 0.45 C5

23 October 2005

0102030

405060

C1 CAF C3 C4 C5 CWB

Rai

nfal

l (m

m)

25 October 2005

010203040506070

C 1 C 3 C AF C 4 C 5 C WB C FR

Rai

nfa

ll (m

m)

7 December 2005

0

20

40

60

80

C1 C3 AF C4 C5 WB FRR

ainf

all (

mm

)

ConclusionsA. Rainfall temporal

distributions

Over the nested catchments• From 24 rain events only in 4 rain events one catchment

have relatively high correlations (r≥ 0.7) to the rest of other catchments which might showed temporally homogenous pattern of rain

• From distances between catchments (Table 9) it can be concluded that rain pattern showed some correlations with r ≥ 0.7 only on the distances < 500 m.

Rainfall temporal distributions

• the longest time lags during rain events were 28 minutes and time lags when rain fell homogenously were only < 6 minutes. The rainfall maximum time lags between the catchments (28 minutes) could be considered as relatively short.

• Rain in catchments area generally fell suddenly, on relatively short time (between 12 to 150 minutes), in the afternoon or late afternoon (13:00 to 17:00) and often spread in patches; those characteristics indicated that types of rain were convective. Convective rain developed because of local surface heating.

Over Sumber Jaya catchment• In general rain occurred on longer time and higher

intensity (2 – 6 mm/2 min) on upper part of the catchment compared to the lower part (the nested catchments); they lasted from 150 -540 minutes; and preceded and ended with light rain.

• Since rain covered mostly the upper part of catchment and did not pour homogenously over the whole catchment, the rains probably were orographic rain. Air masses which moved horizontally were forced to lift because of topographic barriers.

• Stations with distances < 2 km are constantly had high relation (r >0.8); even though up to ≈ 17 km there was still exist some correlation (r ≈ 0.5). It can be concluded that rainfall distributions inside Sumber Jaya catchment from July to December were not homogenously covered the whole area and this could mean that moisture that came form uplifting movement due to topographic barrier only yield in local rain around the mountains.

• Time lags between the two stations were about 15 minutes. Probably time lags were not the important substances on this analysis since moisture came from different sources; not from one source and then moved to another area. The time lags did not reflect the time of storm moving from one source with certain directions.

Over the nested catchments

• In general source of rainfall in this catchment area mostly were not originated from single cloud cluster, rain was not centred in one area and spread with lower intensity to the surrounding area. It was most likely that small cluster of clouds were spread over the catchments, then grew and some times one cluster might dominated the area for short time.

• Only occasionally that rainfall in this area formed by one big cluster of cloud and continually dominated the area. This is related to what was explained on previous section that rain type over the catchments was convective type which developed from surface heating. The spread of the clouds could also reflect the uneven heating on catchments surface.

• larger clusters mostly developed over catchment WB and over catchment 4 and 5. Hence, higher rain depths occurred on the down part (outlet) of the catchment, and sometimes on the middle part but rarely from the upper part.

• The catchments outlet (catchment WB) was closer to Mount Subhan (West part of the Sumber Jaya catchment) while catchment 1 was closer to Bukit Rigis area (central part of the catchment). Forest in Mount Subhan was in better coverage compared to Bukit Rigis, Bukit Rigis are the area of intense coffee plantations, consequently, Subhan were a better moisture sources than Bukit Rigis.

Rainfall spatial distributions

Over Sumber Jaya catchment

The results show that most of the rains started from and had high depth at Subhan Mountain area (West, 1623 m asl). The other moisture sources were Mount Benatan (North, 1688m asl) and Bukit Rigis (Central, 1395 m asl). From geographic position of Sumber Jaya region, Mount Subhan is the highest elevation which face the open ocean at the west of Lampung Province, and behind Subhan is Benatan.

The actual of rain season, when rain sources came from large system (the Indonesian ocean) not just came from local surface heating, occurred on January. It can be tracked from result on January 4th 2006 when rain covered the whole catchment and consistently the source came from Mount Subhan.

Thank you