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\begin{document}

\title{A unique data set from southern Africa's mesic high-altitude fire climax
grasslands: The Cathedral Peak experimental catchments from 1948 onwards}



\author[1]{Michele Toucher}%
\author[1]{Kent Lawrence}%
\author[1]{Susan Janse van Rensburg}%
\author[1]{Paul Gordijn}%
\affil[1]{South African Environmental Observation Network}%


\vspace{-1em}



  
  \date{June 16, 2024}


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\textbf{1. SITE DESCRIPTION}

The Cathedral Peak research catchments, which form part of a strategic
water source area for South Africa, consist of ten (named I -- X) well
defined hydrological catchments, ranging in altitude from 1 820 m.a.s.l
to 2 463 m.a.s.l (Figure 1). The catchments fall within the summer
rainfall region of South Africa, experiencing wet, humid summers and
cold, dry winters (Everson \emph{et al} ., 1998). The mean annual
precipitation (MAP) for the area is approximately 1 400 mm (Bosch,
1979), with 84 \% of this rainfall occurring between the months of
October and March (Schulze, 1976). Half of the rainfall events in the
catchments are thunderstorms (Schulze, 1976). Approximately 49 \% of the
rainfall is converted to streamflow, with two thirds of the streamflow
yield occurring during the four months from January to April (Bosch,
1979). The natural vegetation of the catchments is fire-adapted montane
grassland, dominated by the grass (\emph{Themeda triandra)} . Woody
communities dominated by \emph{Leucosidea sericea} and \emph{Buddleia
salvifolia} occur in narrow, fire-protected zones along the streams in
some catchments (Bosch, 1979).

\textbf{Figure 1}

\textbf{2. HISTORICAL MONITORING IN THE CATHEDRAL PEAK RESEARCH
CATCHMENTS}

Historically, the Mike's Pass station (1948 -- 1994) was the primary
meteorological station for the research catchments (Figure 1). In
addition, precipitation was monitored at twenty-five sites across
catchments I -- X. Both 5'' Snowdon rain gauges with Nipher shields and
5 \& 1/16'' Casella Snowdon recording rain gauges were used. Streamflow
monitoring was initiated in Catchments I -- IX during the late 1940's
and 1950's, and Catchment X during the 1960's. At the outlet of each
catchment a concrete weir and stilling hut, with 90 degree V Notches, 18
inches deep, surmounted by 6 feet wide rectangular notches of varying
depth (Meyburgh \emph{et al.,} 1970) made of brass were installed. The
stilling ponds were dug to bedrock and rock walls for the pond were
constructed. Details of how early measurements were taken, error checked
and processed are given in Myeburgh \emph{et al.} (1970). When cleaning
the weirs, qualitative observations on the volume of silt removed from
the weirs were made for selected catchments. Water chemistry sampling
was initiated in Cathedral Peak in 1981, samples were analysed for
Na\textsuperscript{+}, K\textsuperscript{+}, Ca\textsuperscript{+},
Mg\textsuperscript{+}, Cl\textsuperscript{-},
SO\textsubscript{4}\textsuperscript{2-}, HCO\textsubscript{3},
NH\textsubscript{4}\textsuperscript{+},
PO\textsubscript{4}\textsuperscript{3-},
NO\textsubscript{3}\textsuperscript{-}, TP (Total Phosphorus), KN, Si
and F. The pH and conductivity levels were assessed on site. A wealth of
data has been collected for the Cathedral Peak research catchments, with
the Council for Scientific and Industrial Research (CSIR) being the
custodian of the hydrological and climatological data sets until SAEON's
involvement in the catchments from 2012 onwards.

\textbf{3. CURRENT RESEARCH PLAN, MONITORING AND DATA}

Water is considered one of South Africa's potentially key limiting
factors for economic development. Falling within a strategic water
source, the Cathedral Peak Long-Term Ecological Research (LTER) platform
is unique in that it is the only high-altitude hydroclimatic monitoring
site in the southern African region. Thus, addressing the need for
quality, long-term datasets and process level understanding in sensitive
high-altitude areas, which are needed to improve the understanding of
global change impacts on the ecosystem to ensure water security and
provision to lower lying areas.

The hydro-climatological monitoring network was designed to be
comparable with the historical network to benefit from the historic data
for environmental change research as well as being relevant for
monitoring changes and thresholds or tipping points in system behaviour
into the future. Comparison studies between historical and current
monitoring equipment have been undertaken (Gray and Toucher, 2019). More
intensive monitoring is undertaken in Catchment VI, a near `pristine'
grassland catchment which is considered as the core, benchmark catchment
as well as in Catchment III which is degraded and fire-protected
Catchment IX which has become encroached with woody species.

3.1 Climatological monitoring

An automatic weather station (AWS) was installed at the old Mike's Pass
meteorological site (1860 m.a.s.l) in August 2012. At this site, the
core climatological parameters of solar radiation (CMP3, Kipp \& Zonen,
Delft, The Netherlands), wind speed and direction (Model 03002, R.M.
Young, Traverse city, Michigan, USA), air temperature and humidity
(CS215, Campbell Scientific Inc., Logan, Utah, USA), rainfall (TR-525,
Texas Electronics Inc., Dallas, Texas, USA) are monitored. The climatic
data are averaged over 5-min intervals from observations made every 10 s
and stored on a datalogger (CR1000, Campbell Scientific Inc., Logan,
Utah, USA). The rain gauge orifice is at 1.2 m above the ground and all
other sensors are located 2 m above the ground. Two additional rain
gauges (TR-525, Texas Electronics Inc., Dallas, Texas, USA with a Hobo
Pendant Event loggers UA-003-64, MA, USA) are installed at the site as
well as a ground-level rain gauge designed to World Meteorological
Organisation specifications, to ensure the quality of the rainfall
record. Fog is monitored using a Juvick type gauge. Barometric pressure
(PTB110, Viasala, Vantaa, Helsinki, Finland) and ground surface
temperature (T107L, Campbell Scientific Inc., Logan, Utah, USA) are also
recorded. Two additional AWS, one at a higher altitude of 3010 m.a.s.l
(Vulture's retreat) and another at a lower altitude of 1367 m.a.s.l (OIC
Research office), measure the same core climatological parameters as the
Mike's Pass AWS.

Through Catchments I -- X, twenty-three rain gauges (TR-525, Texas
Electronics Inc., Dallas, Texas, USA with a Hobo Pendant Event loggers
UA-003-64, MA, USA), at a standard height of 1.2 m, have been installed
at the sites where the historic rain gauges were located.

3.2 Energy balance and carbon flux monitoring

Fluxes and the energy balance are monitored in the near pristine
Catchment VI with a full open path eddy covariance (EC) system (OPEC,
Campbell Scientific Inc., Logan, Utah, USA), and alongside this soil
respiration is monitored with a Li-Cor8100 equipped with eight chambers.
Complimented by monthly soil respiration measurements across Catchment
III and IX using cost effective techniques. A Large Aperture
Scintillometer was installed for a short period in Catchment VI as well.
The energy balance components are monitored in Catchments III and IX for
use in the Surface Renewal method to solve for total evaporation.

3.3 Hydrological and soil water monitoring

Streamflow monitoring has resumed at the outlets of catchments III, IV,
V, VI, VII and IX. The original weirs and stilling huts were repaired,
and water stage-height is monitored using an Orpheus Mini (Ott Hydromet
GmbH, Germany) at weirs IV, V, VI and VII, and CS451 Stainless steel
SDI-12 Pressure Transducers and with CR200 loggers at weirs III, VI and
IX. The two pressure transducers installed at weir VI are to ensure the
quality of streamflow records from the core catchment. Water quality
measurements of EC, TDS, PH, DO, ORP and temperature are taken on a
monthly basis using a YSI Professional Plus multi-probe at each of the
monitored weirs, including water sample collections for DOC. Soil water
is monitored continuously in Catchment VI using a Cosmic Ray Probe for
spatial soil water and CS616 Water Content Reflectometers installed to a
depth of 1.4 m at the EC tower. In Catchments III and IX soil water is
monitored using CS616 Water Content Reflectometers at the site of the
energy balance measurements. Complementary spatially distributed,
monthly measurements of soil water are made using a Diviner 2000
(Sentek). Soil surveys have been undertaken as well.

\textbf{4. CONTRIBUTIONS AND APPLICATIONS OF THE DATA}

The catchments have been instrumental in the development of South
Africa's hydrological and ecological research, and have provided the
evidence base for much of the country's water, forestry and
environmental policy. In particular, the data from the catchments has
contributed to the understanding of the impacts of afforestation on
water yield (e.g. N\selectlanguage{ngerman}änni, 1970a, b; Bosch 1979; van der Zel, 1995, Scott
\& Smith, 1997) hydrological model development (Schulze, 1976; Schulze,
1995) and understanding the impacts of fire on streamflow (Nänni, 1960;
Bosch \emph{et al} ., 1984; Van Wyk, 1986). The historical data
collected for the site was consistent and of high quality until 1985
when funding for the monitoring became constrained. Due to the data gap
between 1991 and 2012 and the short record since monitoring resumed, no
trend analysis has been undertaken. However, the monthly rainfall and
streamflow records expressed as an anomaly from the monthly means of the
historical period (1951 -- 1980) indicate that the contemporary period
has been drier than the historical records (Figure 2). The 2018/2019
summer was one of the driest summers on record for Mike's Pass
meteorological station.

\textbf{Figure 2}

The Cathedral Peak catchments fall within the Northern Drakensberg
Strategic Water Source Area which generates 4.94\% of South Africa's
mean annual runoff (Le Maitre et al., 2018). Being the only high
altitude monitored catchments on the eastern escarpment, the long term
data from these catchments is of paramount importance in determining the
impacts of environmental change on the ability of the area to supply
water resources. The historic and contemporary records from these
catchments provide data from Africa, which is often difficult to access
even locally, and is scarcely represented in global analyses and
international insights inferences that seek to influence policy and
practice that affect Africa. Improving access to and inclusion of the
African data and insights that are contextually relevant is critical for
the development of locally beneficial policy and practice, and avoids
negative outcomes of well-intended policies based on data from
elsewhere.

\textbf{5. DATA AVAILABILITY}

The Cathedral Peak research catchments have been registered as LTER site
(\emph{https://deims.org/495a527c-4b57-4daa-b783-9b1e016dbaec}) and
SAEON is focused on ensuring the longevity and quality of the data. The
Mike's Pass AWS can be viewed
at\emph{http://gfw.dirisa.org/weather/mikes-pass-weather-station}and the
higher altitude station
at\emph{http://gfw.dirisa.org/weather/vultures-retreat-weather-station}.
The contemporary daily precipitation
(https://doi.org/10.15493/SAEON.GFW.10000002), streamflow
(https://doi.org/10.15493/SAEON.GFW.10000007), and fog
(https://doi.org/10.15493/SAEON.GFW.10000009) records are publicly
available. The data will be made publicly accessible, through the SAEON
Observations Database (\emph{https://observations.saeon.ac.za/}) which
is still under development. Specific project based data will be made
publicly available following an embargo period.

\textbf{References}

Bosch, J M. (1979). Treatment effects on annual and dry period
streamflow at Cathedral Peak. \emph{South African Forestry
Journal,}108(1), 29-38.

Bosch, J M., Schulze, R E. \& Kruger, F J. (1984). The effect of fire on
water yield. In Booysen, J de V. \& Tainton, N M. (Eds), \emph{The
Ecological Effects of Fire in South African Ecosystems} . Springer,
Berlin.

Everson, C E., Molefe, G L.\& Everson, T M. (1998) Monitoring and
modelling components of the water balance in a grassland catchment in
the summer rainfall area of South Africa. Water Research Commission,
RSA, Report 493/1/98.

Gray, B. \& Toucher, M L. (2019). Rain gauge accuracy at a high-altitude
meteorological station in Cathedral Peak. \emph{Journal of Hydrologic
Engineering} , 24 (2), 04018064.

Nänni, U W. (1960). The immediate effects of veld-burning on streamflow
in Cathedral Peak catchments. \emph{Journal of the South African
Forestry Association} , 34(1), 7-12.

Nänni, U W. (1970a). The effect of afforestation on streamflow at
Cathedral Peak: Report No. 1. \emph{South African Forestry Journal} ,
74(1), 6-12.

Nänni, U W. (1970b). Trees, water and perspective. \emph{South African
Forestry Journal} , 75(1), 9-17.

SAEON Grasslands-Forests-Wetlands Node. (2020). Cathedral Peak research
catchments Mike`s Pass Station Fog Data {[}Data set{]}. South African
Environmental Observation Network.
https://doi.org/10.15493/SAEON.GFW.10000009

SAEON Grasslands-Forests-Wetlands Node. (2020). Cathedral Peak research
catchments contemporary daily rainfall dataset {[}Data set{]}. South
African Environmental Observation Network.
https://doi.org/10.15493/SAEON.GFW.10000002

SAEON Grasslands-Forests-Wetlands Node. (2020). Cathedral Peak research
catchments contemporary daily streamflow dataset {[}Data set{]}. South
African Environmental Observation Network.
https://doi.org/10.15493/SAEON.GFW.10000007

Schulze, R E. (1975). Catchment evapotranspiration in the Natal
Drakensberg. Unpublished PhD Thesis, University of Natal,
Pietermaritzburg, South Africa. Pp 244.

Schulze, R E. (1976). On the application of trend surfaces of
precipitation to mountainous areas. \emph{Water SA} , 2(3), 110-118.

Scott, D F. \& Smith, R E. (1997). Preliminary empirical models to
predict reductions in total and lowflows resulting from
afforestation.\emph{Water SA} , 23, 135-140.

van der Zel, D W. (1995). Accomplishments and dynamics of the South
African afforestation permit system. \emph{South African Forestry
Journal} , 172, 49-57.

Van Wyk, D B. (1986). The effects of catchment management on sediment
and nutrient exports in the Natal Drakensberg. In Schulze, R E. (Ed),
Proc. Second South African National Hydrology Symp., Pietermaritzburg,
September 1985. Agricultural Catchments Res. Unit Rep. No. 22,
Department of Agricultural Engineering, University of Natal,
Pietermaritzburg, pp. 266 -- 274.

\textbf{Figure Captions}

Figure 1: Location of the Cathedral Peak Research catchments, South
Africa and the monitoring sites in the catchments

Figure 2: (a) Monthly rainfall from the Mike's Pass AWS and (b)
Catchment VI streamflow records expressed as an anomaly from the monthly
means of the historical period (1951 -- 1980)\selectlanguage{english}
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